Set the language on `TAPi18n` when user selects language

When the `TAPi18n` initialization code was removed from an `autorun()`
it no longer is rerun when a user's profile language is changed.

client/components/users/userHeader.js

@@ -213,6 +213,7 @@ Template.changeLanguagePopup.events({
         'profile.language': this.tag,
       },
     });
+    TAPi18n.setLanguage(this.tag);
     event.preventDefault();
   },
 });