UX: Add translations for lightbox

app/assets/javascripts/discourse/lib/lightbox.js.es6

@@ -20,7 +20,16 @@ export default function($elem) {
         mainClass: "mfp-zoom-in",
 
         gallery: {
-          enabled: true
+          enabled: true,
+          tPrev: I18n.t("lightbox.previous"),
+          tNext: I18n.t("lightbox.next"),
+          tCounter: I18n.t("lightbox.counter")
+        },
+
+        tClose: I18n.t("lightbox.close"),
+        tLoading: I18n.t("lightbox.loading"),
+        ajax: {
+          tError: I18n.t("lightbox.content_load_error")
         },
 
         callbacks: {
@@ -57,6 +66,7 @@ export default function($elem) {
         },
 
         image: {
+          tError: I18n.t("lightbox.image_load_error"),
           titleSrc(item) {
             const href = item.el.data("download-href") || item.src;
             let src = [

config/locales/client.en.yml

@@ -2802,6 +2802,13 @@ en:
 
     lightbox:
       download: "download"
+      previous: "Previous (Left arrow key)"
+      next: "Next (Right arrow key)"
+      counter: "%curr% of %total%"
+      close: "Close (Esc)"
+      loading: "Loading…"
+      content_load_error: '<a href="%url%">The content</a> could not be loaded.'
+      image_load_error: '<a href="%url%">The image</a> could not be loaded.'
 
     keyboard_shortcuts_help:
       title: "Keyboard Shortcuts"