Fall back to "... in [en]" if language name isn't available

The placeholders use two messages, one being language aware and one
not. The tooltips behind the [?] icons do not. A possible solution
would be to do the same and use two messages.

But:
1. Completely removing the information could be confusing,
   escpecially if you have a Babel box and are prompted for
   multiple languages.
2. I don't want to introduce new messages at the moment since we
   are going to redesign the whole thing anyway.
3. It's not really relevant since this only happens in environments
   where ULS is not available (e.g. some of our own test
   environments).

Simply falling back to '[en]' instead of 'English' is a decent
workaround, in my opinion. It's the same format as in the watchlist
and log summary lines so users should recognize it.

Change-Id: I32a893bed54454ef4b0a947a85d0b78f06d5aa95
Merge "Fall back to "... in [en]" if language name isn't available"