diff --git a/CHANGES b/CHANGES
index 9ad92038d..639f7a43a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -38,6 +38,8 @@ Bugs fixed
 * #3873: Failure of deprecation warning mechanism of
   ``sphinx.util.compat.Directive``
 * #3874: Bogus warnings for "citation not referenced" for cross-file citations
+* #3833: command line messages are translated unintentionally with ``language``
+  setting.
 
 Testing
 --------
diff --git a/setup.cfg b/setup.cfg
index 560bde328..e0312ce00 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -9,7 +9,7 @@ upload = upload --sign --identity=36580288
 [extract_messages]
 mapping_file = babel.cfg
 output_file = sphinx/locale/sphinx.pot
-keywords = _ l_ lazy_gettext
+keywords = _ __ l_ lazy_gettext
 
 [update_catalog]
 input_file = sphinx/locale/sphinx.pot
diff --git a/sphinx/application.py b/sphinx/application.py
index c06e86995..27dfeb2e4 100644
--- a/sphinx/application.py
+++ b/sphinx/application.py
@@ -34,7 +34,7 @@ from sphinx.environment import BuildEnvironment
 from sphinx.events import EventManager
 from sphinx.extension import verify_required_extensions
 from sphinx.io import SphinxStandaloneReader
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.registry import SphinxComponentRegistry
 from sphinx.util import pycompat  # noqa: F401
 from sphinx.util import import_object
@@ -179,8 +179,8 @@ class Sphinx(object):
         # check the Sphinx version if requested
         if self.config.needs_sphinx and self.config.needs_sphinx > sphinx.__display_version__:
             raise VersionRequirementError(
-                _('This project needs at least Sphinx v%s and therefore cannot '
-                  'be built with this version.') % self.config.needs_sphinx)
+                __('This project needs at least Sphinx v%s and therefore cannot '
+                   'be built with this version.') % self.config.needs_sphinx)
 
         # set confdir to srcdir if -C given (!= no confdir); a few pieces
         # of code expect a confdir to be set
@@ -206,9 +206,9 @@ class Sphinx(object):
                 self.config.setup(self)
             else:
                 raise ConfigError(
-                    _("'setup' as currently defined in conf.py isn't a Python callable. "
-                      "Please modify its definition to make it a callable function. This is "
-                      "needed for conf.py to behave as a Sphinx extension.")
+                    __("'setup' as currently defined in conf.py isn't a Python callable. "
+                       "Please modify its definition to make it a callable function. This is "
+                       "needed for conf.py to behave as a Sphinx extension.")
                 )
 
         # now that we know all config values, collect them from conf.py
@@ -220,7 +220,7 @@ class Sphinx(object):
         # check primary_domain if requested
         primary_domain = self.config.primary_domain
         if primary_domain and not self.registry.has_domain(primary_domain):
-            logger.warning(_('primary_domain %r not found, ignored.'), primary_domain)
+            logger.warning(__('primary_domain %r not found, ignored.'), primary_domain)
 
         # create the builder
         self.builder = self.create_builder(buildername)
@@ -257,7 +257,7 @@ class Sphinx(object):
         if self.config.language is not None:
             if has_translation or self.config.language == 'en':
                 # "en" never needs to be translated
-                logger.info(_('done'))
+                logger.info(__('done'))
             else:
                 logger.info('not available for built-in messages')
 
@@ -278,19 +278,19 @@ class Sphinx(object):
                 self.env.domains[domain.name] = domain
         else:
             try:
-                logger.info(bold(_('loading pickled environment... ')), nonl=True)
+                logger.info(bold(__('loading pickled environment... ')), nonl=True)
                 filename = path.join(self.doctreedir, ENV_PICKLE_FILENAME)
                 self.env = BuildEnvironment.frompickle(filename, self)
                 self.env.domains = {}
                 for domain in self.registry.create_domains(self.env):
                     # this can raise if the data version doesn't fit
                     self.env.domains[domain.name] = domain
-                logger.info(_('done'))
+                logger.info(__('done'))
             except Exception as err:
                 if isinstance(err, IOError) and err.errno == ENOENT:
-                    logger.info(_('not yet created'))
+                    logger.info(__('not yet created'))
                 else:
-                    logger.info(_('failed: %s'), err)
+                    logger.info(__('failed: %s'), err)
                 self._init_env(freshenv=True)
 
     def preload_builder(self, name):
@@ -300,7 +300,7 @@ class Sphinx(object):
     def create_builder(self, name):
         # type: (unicode) -> Builder
         if name is None:
-            logger.info(_('No builder selected, using default: html'))
+            logger.info(__('No builder selected, using default: html'))
             name = 'html'
 
         return self.registry.create_builder(self, name)
@@ -339,13 +339,13 @@ class Sphinx(object):
                 self.builder.build_update()
 
             status = (self.statuscode == 0 and
-                      _('succeeded') or _('finished with problems'))
+                      __('succeeded') or __('finished with problems'))
             if self._warncount:
-                logger.info(bold(_('build %s, %s warning%s.') %
+                logger.info(bold(__('build %s, %s warning%s.') %
                                  (status, self._warncount,
                                   self._warncount != 1 and 's' or '')))
             else:
-                logger.info(bold(_('build %s.') % status))
+                logger.info(bold(__('build %s.') % status))
         except Exception as err:
             # delete the saved env to force a fresh build next time
             envfile = path.join(self.doctreedir, ENV_PICKLE_FILENAME)
@@ -504,7 +504,7 @@ class Sphinx(object):
         logger.debug('[app] adding config value: %r',
                      (name, default, rebuild) + ((types,) if types else ()))  # type: ignore
         if name in self.config:
-            raise ExtensionError(_('Config value %r already present') % name)
+            raise ExtensionError(__('Config value %r already present') % name)
         if rebuild in (False, True):
             rebuild = rebuild and 'env' or ''
         self.config.add(name, default, rebuild, types)
@@ -516,7 +516,7 @@ class Sphinx(object):
 
     def set_translator(self, name, translator_class):
         # type: (unicode, Type[nodes.NodeVisitor]) -> None
-        logger.info(bold(_('Change of translator for the %s builder.') % name))
+        logger.info(bold(__('Change of translator for the %s builder.') % name))
         self.registry.add_translator(name, translator_class)
 
     def add_node(self, node, **kwds):
@@ -524,8 +524,8 @@ class Sphinx(object):
         logger.debug('[app] adding node: %r', (node, kwds))
         if not kwds.pop('override', False) and \
            hasattr(nodes.GenericNodeVisitor, 'visit_' + node.__name__):
-            logger.warning(_('while setting up extension %s: node class %r is '
-                             'already registered, its visitors will be overridden'),
+            logger.warning(__('while setting up extension %s: node class %r is '
+                              'already registered, its visitors will be overridden'),
                            self._setting_up_extension, node.__name__,
                            type='app', subtype='add_node')
         nodes._add_node_class_names([node.__name__])
@@ -533,8 +533,8 @@ class Sphinx(object):
             try:
                 visit, depart = val
             except ValueError:
-                raise ExtensionError(_('Value for key %r must be a '
-                                       '(visit, depart) function tuple') % key)
+                raise ExtensionError(__('Value for key %r must be a '
+                                        '(visit, depart) function tuple') % key)
             translator = self.registry.translators.get(key)
             translators = []
             if translator is not None:
@@ -580,8 +580,8 @@ class Sphinx(object):
         logger.debug('[app] adding directive: %r',
                      (name, obj, content, arguments, options))
         if name in directives._directives:
-            logger.warning(_('while setting up extension %s: directive %r is '
-                             'already registered, it will be overridden'),
+            logger.warning(__('while setting up extension %s: directive %r is '
+                              'already registered, it will be overridden'),
                            self._setting_up_extension[-1], name,
                            type='app', subtype='add_directive')
         directive = directive_helper(obj, content, arguments, **options)
@@ -591,8 +591,8 @@ class Sphinx(object):
         # type: (unicode, Any) -> None
         logger.debug('[app] adding role: %r', (name, role))
         if name in roles._roles:
-            logger.warning(_('while setting up extension %s: role %r is '
-                             'already registered, it will be overridden'),
+            logger.warning(__('while setting up extension %s: role %r is '
+                              'already registered, it will be overridden'),
                            self._setting_up_extension[-1], name,
                            type='app', subtype='add_role')
         roles.register_local_role(name, role)
@@ -603,8 +603,8 @@ class Sphinx(object):
         # register_canonical_role
         logger.debug('[app] adding generic role: %r', (name, nodeclass))
         if name in roles._roles:
-            logger.warning(_('while setting up extension %s: role %r is '
-                             'already registered, it will be overridden'),
+            logger.warning(__('while setting up extension %s: role %r is '
+                              'already registered, it will be overridden'),
                            self._setting_up_extension[-1], name,
                            type='app', subtype='add_generic_role')
         role = roles.GenericRole(name, nodeclass)
diff --git a/sphinx/config.py b/sphinx/config.py
index 451aa8b0d..02ee529a3 100644
--- a/sphinx/config.py
+++ b/sphinx/config.py
@@ -16,7 +16,7 @@ from six import PY2, PY3, iteritems, string_types, binary_type, text_type, integ
 from typing import Any, NamedTuple, Union
 
 from sphinx.errors import ConfigError
-from sphinx.locale import l_, _
+from sphinx.locale import l_, __
 from sphinx.util import logging
 from sphinx.util.i18n import format_date
 from sphinx.util.osutil import cd
@@ -233,8 +233,8 @@ class Config(object):
         else:
             defvalue = self.values[name][0]
             if isinstance(defvalue, dict):
-                raise ValueError(_('cannot override dictionary config setting %r, '
-                                   'ignoring (use %r to set individual elements)') %
+                raise ValueError(__('cannot override dictionary config setting %r, '
+                                    'ignoring (use %r to set individual elements)') %
                                  (name, name + '.key=value'))
             elif isinstance(defvalue, list):
                 return value.split(',')
@@ -242,13 +242,13 @@ class Config(object):
                 try:
                     return int(value)
                 except ValueError:
-                    raise ValueError(_('invalid number %r for config value %r, ignoring') %
+                    raise ValueError(__('invalid number %r for config value %r, ignoring') %
                                      (value, name))
             elif hasattr(defvalue, '__call__'):
                 return value
             elif defvalue is not None and not isinstance(defvalue, string_types):
-                raise ValueError(_('cannot override config setting %r with unsupported '
-                                   'type, ignoring') % name)
+                raise ValueError(__('cannot override config setting %r with unsupported '
+                                    'type, ignoring') % name)
             else:
                 return value
 
@@ -277,7 +277,8 @@ class Config(object):
                     config.setdefault(realvalname, {})[key] = value
                     continue
                 elif valname not in self.values:
-                    logger.warning(_('unknown config value %r in override, ignoring'), valname)
+                    logger.warning(__('unknown config value %r in override, ignoring'),
+                                   valname)
                     continue
                 if isinstance(value, string_types):
                     config[valname] = self.convert_overrides(valname, value)
@@ -296,7 +297,7 @@ class Config(object):
         if name.startswith('_'):
             raise AttributeError(name)
         if name not in self.values:
-            raise AttributeError(_('No such config value: %s') % name)
+            raise AttributeError(__('No such config value: %s') % name)
         default = self.values[name][0]
         if hasattr(default, '__call__'):
             return default(self)
diff --git a/sphinx/directives/code.py b/sphinx/directives/code.py
index e372762ce..41a593aa3 100644
--- a/sphinx/directives/code.py
+++ b/sphinx/directives/code.py
@@ -16,7 +16,7 @@ from docutils.parsers.rst import Directive, directives
 from docutils.statemachine import ViewList
 
 from sphinx import addnodes
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.util import logging
 from sphinx.util import parselinenos
 from sphinx.util.nodes import set_source_info
@@ -63,7 +63,7 @@ def dedent_lines(lines, dedent, location=None):
         return lines
 
     if any(s[:dedent].strip() for s in lines):
-        logger.warning(_('Over dedent has detected'), location=location)
+        logger.warning(__('Over dedent has detected'), location=location)
 
     new_lines = []
     for line in lines:
@@ -83,7 +83,7 @@ def container_wrapper(directive, literal_node, caption):
     directive.state.nested_parse(ViewList([caption], source=''),
                                  directive.content_offset, parsed)
     if isinstance(parsed[0], nodes.system_message):
-        msg = _('Invalid caption: %s' % parsed[0].astext())
+        msg = __('Invalid caption: %s' % parsed[0].astext())
         raise ValueError(msg)
     caption_node = nodes.caption(parsed[0].rawsource, '',
                                  *parsed[0].children)
@@ -198,7 +198,7 @@ class LiteralIncludeReader(object):
         # type: () -> None
         for option1, option2 in self.INVALID_OPTIONS_PAIR:
             if option1 in self.options and option2 in self.options:
-                raise ValueError(_('Cannot use both "%s" and "%s" options') %
+                raise ValueError(__('Cannot use both "%s" and "%s" options') %
                                  (option1, option2))
 
     def read_file(self, filename, location=None):
@@ -211,10 +211,10 @@ class LiteralIncludeReader(object):
 
                 return text.splitlines(True)
         except (IOError, OSError):
-            raise IOError(_('Include file %r not found or reading it failed') % filename)
+            raise IOError(__('Include file %r not found or reading it failed') % filename)
         except UnicodeError:
-            raise UnicodeError(_('Encoding %r used for reading included file %r seems to '
-                                 'be wrong, try giving an :encoding: option') %
+            raise UnicodeError(__('Encoding %r used for reading included file %r seems to '
+                                  'be wrong, try giving an :encoding: option') %
                                (self.encoding, filename))
 
     def read(self, location=None):
@@ -251,7 +251,7 @@ class LiteralIncludeReader(object):
             analyzer = ModuleAnalyzer.for_file(self.filename, '')
             tags = analyzer.find_tags()
             if pyobject not in tags:
-                raise ValueError(_('Object named %r not found in include file %r') %
+                raise ValueError(__('Object named %r not found in include file %r') %
                                  (pyobject, self.filename))
             else:
                 start = tags[pyobject][1]
@@ -277,12 +277,12 @@ class LiteralIncludeReader(object):
                 if all(first + i == n for i, n in enumerate(linelist)):
                     self.lineno_start += linelist[0]
                 else:
-                    raise ValueError(_('Cannot use "lineno-match" with a disjoint '
-                                       'set of "lines"'))
+                    raise ValueError(__('Cannot use "lineno-match" with a disjoint '
+                                        'set of "lines"'))
 
             lines = [lines[n] for n in linelist if n < len(lines)]
             if lines == []:
-                raise ValueError(_('Line spec %r: no lines pulled from include file %r') %
+                raise ValueError(__('Line spec %r: no lines pulled from include file %r') %
                                  (linespec, self.filename))
 
         return lines
diff --git a/sphinx/environment/__init__.py b/sphinx/environment/__init__.py
index bca779cc4..70fdbaeca 100644
--- a/sphinx/environment/__init__.py
+++ b/sphinx/environment/__init__.py
@@ -44,7 +44,7 @@ from sphinx.util.matching import compile_matchers
 from sphinx.util.parallel import ParallelTasks, parallel_available, make_chunks
 from sphinx.util.websupport import is_commentable
 from sphinx.errors import SphinxError, ExtensionError
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.transforms import SphinxTransformer
 from sphinx.versioning import add_uids, merge_doctrees
 from sphinx.deprecation import RemovedInSphinx17Warning, RemovedInSphinx20Warning
@@ -565,10 +565,10 @@ class BuildEnvironment(object):
         if parallel_available and len(docnames) > 5 and self.app.parallel > 1:
             for ext in itervalues(self.app.extensions):
                 if ext.parallel_read_safe is None:
-                    logger.warning(_('the %s extension does not declare if it is safe '
-                                     'for parallel reading, assuming it isn\'t - please '
-                                     'ask the extension author to check and make it '
-                                     'explicit'), ext.name)
+                    logger.warning(__('the %s extension does not declare if it is safe '
+                                      'for parallel reading, assuming it isn\'t - please '
+                                      'ask the extension author to check and make it '
+                                      'explicit'), ext.name)
                     logger.warning('doing serial read')
                     break
                 elif ext.parallel_read_safe is False:
diff --git a/sphinx/events.py b/sphinx/events.py
index 23353dfdb..99decfff5 100644
--- a/sphinx/events.py
+++ b/sphinx/events.py
@@ -17,7 +17,7 @@ from collections import OrderedDict, defaultdict
 from six import itervalues
 
 from sphinx.errors import ExtensionError
-from sphinx.locale import _
+from sphinx.locale import __
 
 if False:
     # For type annotation
@@ -54,13 +54,13 @@ class EventManager(object):
     def add(self, name):
         # type: (unicode) -> None
         if name in self.events:
-            raise ExtensionError(_('Event %r already present') % name)
+            raise ExtensionError(__('Event %r already present') % name)
         self.events[name] = ''
 
     def connect(self, name, callback):
         # type: (unicode, Callable) -> int
         if name not in self.events:
-            raise ExtensionError(_('Unknown event name: %s') % name)
+            raise ExtensionError(__('Unknown event name: %s') % name)
 
         listener_id = self.next_listener_id
         self.next_listener_id += 1
diff --git a/sphinx/ext/graphviz.py b/sphinx/ext/graphviz.py
index 83d89adf2..a1565a1a7 100644
--- a/sphinx/ext/graphviz.py
+++ b/sphinx/ext/graphviz.py
@@ -25,7 +25,7 @@ from docutils.statemachine import ViewList
 
 import sphinx
 from sphinx.errors import SphinxError
-from sphinx.locale import _
+from sphinx.locale import _, __
 from sphinx.util import logging
 from sphinx.util.i18n import search_image_for_language
 from sphinx.util.osutil import ensuredir, ENOENT, EPIPE, EINVAL
@@ -93,8 +93,8 @@ class Graphviz(Directive):
             document = self.state.document
             if self.content:
                 return [document.reporter.warning(
-                    _('Graphviz directive cannot have both content and '
-                      'a filename argument'), line=self.lineno)]
+                    __('Graphviz directive cannot have both content and '
+                       'a filename argument'), line=self.lineno)]
             env = self.state.document.settings.env
             argument = search_image_for_language(self.arguments[0], env)
             rel_filename, filename = env.relfn2path(argument)
@@ -104,13 +104,13 @@ class Graphviz(Directive):
                     dotcode = fp.read()
             except (IOError, OSError):
                 return [document.reporter.warning(
-                    _('External Graphviz file %r not found or reading '
-                      'it failed') % filename, line=self.lineno)]
+                    __('External Graphviz file %r not found or reading '
+                       'it failed') % filename, line=self.lineno)]
         else:
             dotcode = '\n'.join(self.content)
             if not dotcode.strip():
                 return [self.state_machine.reporter.warning(
-                    _('Ignoring "graphviz" directive without content.'),
+                    __('Ignoring "graphviz" directive without content.'),
                     line=self.lineno)]
         node = graphviz()
         node['code'] = dotcode
@@ -201,8 +201,8 @@ def render_dot(self, code, options, format, prefix='graphviz'):
     except OSError as err:
         if err.errno != ENOENT:   # No such file or directory
             raise
-        logger.warning(_('dot command %r cannot be run (needed for graphviz '
-                         'output), check the graphviz_dot setting'), graphviz_dot)
+        logger.warning(__('dot command %r cannot be run (needed for graphviz '
+                          'output), check the graphviz_dot setting'), graphviz_dot)
         if not hasattr(self.builder, '_graphviz_warned_dot'):
             self.builder._graphviz_warned_dot = {}
         self.builder._graphviz_warned_dot[graphviz_dot] = True
@@ -219,11 +219,11 @@ def render_dot(self, code, options, format, prefix='graphviz'):
         stdout, stderr = p.stdout.read(), p.stderr.read()
         p.wait()
     if p.returncode != 0:
-        raise GraphvizError(_('dot exited with error:\n[stderr]\n%s\n'
-                              '[stdout]\n%s') % (stderr, stdout))
+        raise GraphvizError(__('dot exited with error:\n[stderr]\n%s\n'
+                               '[stdout]\n%s') % (stderr, stdout))
     if not path.isfile(outfn):
-        raise GraphvizError(_('dot did not produce an output file:\n[stderr]\n%s\n'
-                              '[stdout]\n%s') % (stderr, stdout))
+        raise GraphvizError(__('dot did not produce an output file:\n[stderr]\n%s\n'
+                               '[stdout]\n%s') % (stderr, stdout))
     return relfn, outfn
 
 
@@ -233,8 +233,8 @@ def render_dot_html(self, node, code, options, prefix='graphviz',
     format = self.builder.config.graphviz_output_format
     try:
         if format not in ('png', 'svg'):
-            raise GraphvizError(_("graphviz_output_format must be one of 'png', "
-                                  "'svg', but is %r") % format)
+            raise GraphvizError(__("graphviz_output_format must be one of 'png', "
+                                   "'svg', but is %r") % format)
         fname, outfn = render_dot(self, code, options, format, prefix)
     except GraphvizError as exc:
         logger.warning('dot code %r: ' % code + str(exc))
diff --git a/sphinx/ext/imgconverter.py b/sphinx/ext/imgconverter.py
index d69a4411b..d2894b2a3 100644
--- a/sphinx/ext/imgconverter.py
+++ b/sphinx/ext/imgconverter.py
@@ -11,7 +11,7 @@
 import subprocess
 
 from sphinx.errors import ExtensionError
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.transforms.post_transforms.images import ImageConverter
 from sphinx.util import logging
 from sphinx.util.osutil import ENOENT, EPIPE, EINVAL
@@ -43,8 +43,8 @@ class ImagemagickConverter(ImageConverter):
             else:
                 return False
         except (OSError, IOError):
-            logger.warning(_('convert command %r cannot be run.'
-                             'check the image_converter setting'),
+            logger.warning(__('convert command %r cannot be run.'
+                              'check the image_converter setting'),
                            self.config.image_converter)
             return False
 
@@ -60,8 +60,8 @@ class ImagemagickConverter(ImageConverter):
         except OSError as err:
             if err.errno != ENOENT:  # No such file or directory
                 raise
-            logger.warning(_('convert command %r cannot be run.'
-                             'check the image_converter setting'),
+            logger.warning(__('convert command %r cannot be run.'
+                              'check the image_converter setting'),
                            self.config.image_converter)
             return False
 
@@ -73,8 +73,8 @@ class ImagemagickConverter(ImageConverter):
             stdout, stderr = p.stdout.read(), p.stderr.read()
             p.wait()
         if p.returncode != 0:
-            raise ExtensionError(_('convert exited with error:\n'
-                                   '[stderr]\n%s\n[stdout]\n%s') %
+            raise ExtensionError(__('convert exited with error:\n'
+                                    '[stderr]\n%s\n[stdout]\n%s') %
                                  (stderr, stdout))
 
         return True
diff --git a/sphinx/ext/mathbase.py b/sphinx/ext/mathbase.py
index 9ca81d738..baa4df176 100644
--- a/sphinx/ext/mathbase.py
+++ b/sphinx/ext/mathbase.py
@@ -13,7 +13,7 @@ from docutils import nodes, utils
 from docutils.parsers.rst import Directive, directives
 
 from sphinx.roles import XRefRole
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.domains import Domain
 from sphinx.util.nodes import make_refnode, set_source_info
 
@@ -103,7 +103,7 @@ class MathDomain(Domain):
         equations = self.data['objects']
         if labelid in equations:
             path = env.doc2path(equations[labelid][0])
-            msg = _('duplicate label of equation %s, other instance in %s') % (labelid, path)
+            msg = __('duplicate label of equation %s, other instance in %s') % (labelid, path)
             raise UserWarning(msg)
         else:
             eqno = self.get_next_equation_number(docname)
diff --git a/sphinx/extension.py b/sphinx/extension.py
index c3b3b901e..0520bf564 100644
--- a/sphinx/extension.py
+++ b/sphinx/extension.py
@@ -12,7 +12,7 @@
 from six import iteritems
 
 from sphinx.errors import VersionRequirementError
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.util import logging
 
 if False:
@@ -50,12 +50,12 @@ def verify_required_extensions(app, requirements):
     for extname, reqversion in iteritems(requirements):
         extension = app.extensions.get(extname)
         if extension is None:
-            logger.warning(_('The %s extension is required by needs_extensions settings,'
-                             'but it is not loaded.'), extname)
+            logger.warning(__('The %s extension is required by needs_extensions settings,'
+                              'but it is not loaded.'), extname)
             continue
 
         if extension.version == 'unknown version' or reqversion > extension.version:
-            raise VersionRequirementError(_('This project needs the extension %s at least in '
-                                            'version %s and therefore cannot be built with '
-                                            'the loaded version (%s).') %
+            raise VersionRequirementError(__('This project needs the extension %s at least in '
+                                             'version %s and therefore cannot be built with '
+                                             'the loaded version (%s).') %
                                           (extname, reqversion, extension.version))
diff --git a/sphinx/locale/__init__.py b/sphinx/locale/__init__.py
index 7c0f9b4f9..6c77eeb8b 100644
--- a/sphinx/locale/__init__.py
+++ b/sphinx/locale/__init__.py
@@ -242,6 +242,16 @@ else:
             return message
 
 
+def __(message):
+    # type: (unicode) -> unicode
+    """A dummy wrapper to i18n'ize exceptions and command line messages.
+
+    In future, the messages are translated using LC_MESSAGES or any other
+    locale settings.
+    """
+    return message
+
+
 def init(locale_dirs, language, catalog='sphinx'):
     # type: (List, unicode, unicode) -> Tuple[Any, bool]
     """Look for message catalogs in `locale_dirs` and *ensure* that there is at
diff --git a/sphinx/registry.py b/sphinx/registry.py
index 2efd5e08a..0861575db 100644
--- a/sphinx/registry.py
+++ b/sphinx/registry.py
@@ -19,7 +19,7 @@ from sphinx.errors import ExtensionError, SphinxError, VersionRequirementError
 from sphinx.extension import Extension
 from sphinx.domains import ObjType
 from sphinx.domains.std import GenericObject, Target
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.roles import XRefRole
 from sphinx.util import logging
 from sphinx.util.docutils import directive_helper
@@ -53,9 +53,9 @@ class SphinxComponentRegistry(object):
     def add_builder(self, builder):
         # type: (Type[Builder]) -> None
         if not hasattr(builder, 'name'):
-            raise ExtensionError(_('Builder class %s has no "name" attribute') % builder)
+            raise ExtensionError(__('Builder class %s has no "name" attribute') % builder)
         if builder.name in self.builders:
-            raise ExtensionError(_('Builder %r already exists (in module %s)') %
+            raise ExtensionError(__('Builder %r already exists (in module %s)') %
                                  (builder.name, self.builders[builder.name].__module__))
         self.builders[builder.name] = builder
 
@@ -69,22 +69,22 @@ class SphinxComponentRegistry(object):
             try:
                 entry_point = next(entry_points)
             except StopIteration:
-                raise SphinxError(_('Builder name %s not registered or available'
-                                    ' through entry point') % name)
+                raise SphinxError(__('Builder name %s not registered or available'
+                                     ' through entry point') % name)
 
             self.load_extension(app, entry_point.module_name)
 
     def create_builder(self, app, name):
         # type: (Sphinx, unicode) -> Builder
         if name not in self.builders:
-            raise SphinxError(_('Builder name %s not registered') % name)
+            raise SphinxError(__('Builder name %s not registered') % name)
 
         return self.builders[name](app)
 
     def add_domain(self, domain):
         # type: (Type[Domain]) -> None
         if domain.name in self.domains:
-            raise ExtensionError(_('domain %s already registered') % domain.name)
+            raise ExtensionError(__('domain %s already registered') % domain.name)
         self.domains[domain.name] = domain
 
     def has_domain(self, domain):
@@ -99,30 +99,30 @@ class SphinxComponentRegistry(object):
     def override_domain(self, domain):
         # type: (Type[Domain]) -> None
         if domain.name not in self.domains:
-            raise ExtensionError(_('domain %s not yet registered') % domain.name)
+            raise ExtensionError(__('domain %s not yet registered') % domain.name)
         if not issubclass(domain, self.domains[domain.name]):
-            raise ExtensionError(_('new domain not a subclass of registered %s '
-                                   'domain') % domain.name)
+            raise ExtensionError(__('new domain not a subclass of registered %s '
+                                    'domain') % domain.name)
         self.domains[domain.name] = domain
 
     def add_directive_to_domain(self, domain, name, obj,
                                 has_content=None, argument_spec=None, **option_spec):
         # type: (unicode, unicode, Any, bool, Any, Any) -> None
         if domain not in self.domains:
-            raise ExtensionError(_('domain %s not yet registered') % domain)
+            raise ExtensionError(__('domain %s not yet registered') % domain)
         directive = directive_helper(obj, has_content, argument_spec, **option_spec)
         self.domains[domain].directives[name] = directive
 
     def add_role_to_domain(self, domain, name, role):
         # type: (unicode, unicode, Any) -> None
         if domain not in self.domains:
-            raise ExtensionError(_('domain %s not yet registered') % domain)
+            raise ExtensionError(__('domain %s not yet registered') % domain)
         self.domains[domain].roles[name] = role
 
     def add_index_to_domain(self, domain, index):
         # type: (unicode, Type[Index]) -> None
         if domain not in self.domains:
-            raise ExtensionError(_('domain %s not yet registered') % domain)
+            raise ExtensionError(__('domain %s not yet registered') % domain)
         self.domains[domain].indices.append(index)
 
     def add_object_type(self, directivename, rolename, indextemplate='',
@@ -157,7 +157,7 @@ class SphinxComponentRegistry(object):
     def add_source_parser(self, suffix, parser):
         # type: (unicode, Parser) -> None
         if suffix in self.source_parsers:
-            raise ExtensionError(_('source_parser for %r is already registered') % suffix)
+            raise ExtensionError(__('source_parser for %r is already registered') % suffix)
         self.source_parsers[suffix] = parser
 
     def get_source_parsers(self):
@@ -184,8 +184,8 @@ class SphinxComponentRegistry(object):
         if extname in app.extensions:  # alread loaded
             return
         if extname in EXTENSION_BLACKLIST:
-            logger.warning(_('the extension %r was already merged with Sphinx since '
-                             'version %s; this extension is ignored.'),
+            logger.warning(__('the extension %r was already merged with Sphinx since '
+                              'version %s; this extension is ignored.'),
                            extname, EXTENSION_BLACKLIST[extname])
             return
 
@@ -195,12 +195,12 @@ class SphinxComponentRegistry(object):
         try:
             mod = __import__(extname, None, None, ['setup'])
         except ImportError as err:
-            logger.verbose(_('Original exception:\n') + traceback.format_exc())
-            raise ExtensionError(_('Could not import extension %s') % extname, err)
+            logger.verbose(__('Original exception:\n') + traceback.format_exc())
+            raise ExtensionError(__('Could not import extension %s') % extname, err)
 
         if not hasattr(mod, 'setup'):
-            logger.warning(_('extension %r has no setup() function; is it really '
-                             'a Sphinx extension module?'), extname)
+            logger.warning(__('extension %r has no setup() function; is it really '
+                              'a Sphinx extension module?'), extname)
             metadata = {}  # type: Dict[unicode, Any]
         else:
             try:
@@ -208,9 +208,9 @@ class SphinxComponentRegistry(object):
             except VersionRequirementError as err:
                 # add the extension name to the version required
                 raise VersionRequirementError(
-                    _('The %s extension used by this project needs at least '
-                      'Sphinx v%s; it therefore cannot be built with this '
-                      'version.') % (extname, err)
+                    __('The %s extension used by this project needs at least '
+                       'Sphinx v%s; it therefore cannot be built with this '
+                       'version.') % (extname, err)
                 )
 
         if metadata is None:
@@ -218,9 +218,9 @@ class SphinxComponentRegistry(object):
             if extname == 'rst2pdf.pdfbuilder':
                 metadata['parallel_read_safe'] = True
         elif not isinstance(metadata, dict):
-            logger.warning(_('extension %r returned an unsupported object from '
-                             'its setup() function; it should return None or a '
-                             'metadata dictionary'), extname)
+            logger.warning(__('extension %r returned an unsupported object from '
+                              'its setup() function; it should return None or a '
+                              'metadata dictionary'), extname)
 
         app.extensions[extname] = Extension(extname, mod, **metadata)
         app._setting_up_extension.pop()
diff --git a/sphinx/theming.py b/sphinx/theming.py
index 7a11f4bbf..1cd07b8dc 100644
--- a/sphinx/theming.py
+++ b/sphinx/theming.py
@@ -23,7 +23,7 @@ from six.moves import configparser
 from sphinx import package_dir
 from sphinx.deprecation import RemovedInSphinx20Warning
 from sphinx.errors import ThemeError
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.util import logging
 from sphinx.util.osutil import ensuredir
 
@@ -80,15 +80,15 @@ class Theme(object):
         try:
             inherit = self.config.get('theme', 'inherit')
         except configparser.NoSectionError:
-            raise ThemeError(_('theme %r doesn\'t have "theme" setting') % name)
+            raise ThemeError(__('theme %r doesn\'t have "theme" setting') % name)
         except configparser.NoOptionError:
-            raise ThemeError(_('theme %r doesn\'t have "inherit" setting') % name)
+            raise ThemeError(__('theme %r doesn\'t have "inherit" setting') % name)
 
         if inherit != 'none':
             try:
                 self.base = factory.create(inherit)
             except ThemeError:
-                raise ThemeError(_('no theme named %r found, inherited by %r') %
+                raise ThemeError(__('no theme named %r found, inherited by %r') %
                                  (inherit, name))
 
     def get_theme_dirs(self):
@@ -113,8 +113,8 @@ class Theme(object):
                 return self.base.get_config(section, name, default)
 
             if default is NODEFAULT:
-                raise ThemeError(_('setting %s.%s occurs in none of the '
-                                   'searched theme configs') % (section, name))
+                raise ThemeError(__('setting %s.%s occurs in none of the '
+                                    'searched theme configs') % (section, name))
             else:
                 return default
 
@@ -234,7 +234,7 @@ class HTMLThemeFactory(object):
             if callable(target):
                 themedir = target()
                 if not isinstance(themedir, string_types):
-                    logger.warning(_('Theme extension %r does not respond correctly.') %
+                    logger.warning(__('Theme extension %r does not respond correctly.') %
                                    entry_point.module_name)
             else:
                 themedir = target
@@ -261,8 +261,8 @@ class HTMLThemeFactory(object):
                     name = entry[:-4]
                     themes[name] = pathname
                 else:
-                    logger.warning(_('file %r on theme path is not a valid '
-                                     'zipfile or contains no theme'), entry)
+                    logger.warning(__('file %r on theme path is not a valid '
+                                      'zipfile or contains no theme'), entry)
             else:
                 if path.isfile(path.join(pathname, THEMECONF)):
                     themes[entry] = pathname
@@ -277,11 +277,11 @@ class HTMLThemeFactory(object):
 
         if name not in self.themes:
             if name == 'sphinx_rtd_theme':
-                raise ThemeError(_('sphinx_rtd_theme is no longer a hard dependency '
-                                   'since version 1.4.0. Please install it manually.'
-                                   '(pip install sphinx_rtd_theme)'))
+                raise ThemeError(__('sphinx_rtd_theme is no longer a hard dependency '
+                                    'since version 1.4.0. Please install it manually.'
+                                    '(pip install sphinx_rtd_theme)'))
             else:
-                raise ThemeError(_('no theme named %r found '
-                                   '(missing theme.conf?)') % name)
+                raise ThemeError(__('no theme named %r found '
+                                    '(missing theme.conf?)') % name)
 
         return Theme(name, self.themes[name], factory=self)
diff --git a/sphinx/transforms/post_transforms/__init__.py b/sphinx/transforms/post_transforms/__init__.py
index 8e2580a2d..4c4e094d1 100644
--- a/sphinx/transforms/post_transforms/__init__.py
+++ b/sphinx/transforms/post_transforms/__init__.py
@@ -17,7 +17,7 @@ from docutils.utils import get_source_line
 from sphinx import addnodes
 from sphinx.deprecation import RemovedInSphinx20Warning
 from sphinx.environment import NoUri
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.transforms import SphinxTransform
 from sphinx.util import logging
 
@@ -135,8 +135,8 @@ class ReferencesResolver(SphinxTransform):
             return None
         if len(results) > 1:
             nice_results = ' or '.join(':%s:' % r[0] for r in results)
-            logger.warning(_('more than one target found for \'any\' cross-'
-                             'reference %r: could be %s'), target, nice_results,
+            logger.warning(__('more than one target found for \'any\' cross-'
+                              'reference %r: could be %s'), target, nice_results,
                            location=node)
         res_role, newnode = results[0]
         # Override "any" class with the actual role type to get the styling
@@ -165,10 +165,10 @@ class ReferencesResolver(SphinxTransform):
         if domain and typ in domain.dangling_warnings:
             msg = domain.dangling_warnings[typ]
         elif node.get('refdomain', 'std') not in ('', 'std'):
-            msg = (_('%s:%s reference target not found: %%(target)s') %
+            msg = (__('%s:%s reference target not found: %%(target)s') %
                    (node['refdomain'], typ))
         else:
-            msg = _('%r reference target not found: %%(target)s') % typ
+            msg = __('%r reference target not found: %%(target)s') % typ
         logger.warning(msg % {'target': target},
                        location=node, type='ref', subtype=typ)
 
diff --git a/sphinx/util/docutils.py b/sphinx/util/docutils.py
index 1fe72af58..c984bcfaf 100644
--- a/sphinx/util/docutils.py
+++ b/sphinx/util/docutils.py
@@ -22,7 +22,7 @@ from docutils.utils import Reporter
 from docutils.parsers.rst import directives, roles, convert_directive_function
 
 from sphinx.errors import ExtensionError
-from sphinx.locale import _
+from sphinx.locale import __
 from sphinx.util import logging
 
 logger = logging.getLogger(__name__)
@@ -193,6 +193,6 @@ def directive_helper(obj, has_content=None, argument_spec=None, **option_spec):
         return convert_directive_function(obj)
     else:
         if has_content or argument_spec or option_spec:
-            raise ExtensionError(_('when adding directive classes, no '
-                                   'additional arguments may be given'))
+            raise ExtensionError(__('when adding directive classes, no '
+                                    'additional arguments may be given'))
         return obj