VOLDEV-27

@Grunny - here, I've cherry picked the two commits from #3482 so that we don't have that big mess. @TK-999 has already LGTM'd these changes, so could this be merged soon please? Thanks ♥
@lizlux: inContentLanguage ensures that the message is translated to the language of the *wiki*, as opposed to the user.

For instance, if a user with their interface in English updated a video on a Hungarian wiki, the edit summary would be "Videó frissítve" - the Hungarian summary - instead of the English one, "updated video".