Add Builder.use_message_catalog flag

sphinx/builders/__init__.py

@@ -57,6 +57,8 @@ class Builder(object):
     versioning_compare = False
     # allow parallel write_doc() calls
     allow_parallel = False
+    # support translation
+    use_message_catalog = True
 
     def __init__(self, app):
         # type: (Sphinx) -> None

sphinx/builders/gettext.py

@@ -113,6 +113,7 @@ class I18nBuilder(Builder):
     name = 'i18n'
     versioning_method = 'text'
     versioning_compare = None  # be set by `gettext_uuid`
+    use_message_catalog = False
 
     def init(self):
         # type: () -> None

sphinx/environment/__init__.py

@@ -430,7 +430,7 @@ class BuildEnvironment(object):
         # is set for the doc source and the mo file, it is processed again from
         # the reading phase when mo is updated. In the future, we would like to
         # move i18n process into the writing phase, and remove these lines.
-        if builder.name != 'gettext':
+        if builder.use_message_catalog:
             # add catalog mo file dependency
             for docname in self.found_docs:
                 catalog_files = find_catalog_files(