Viewing a history listing
Ok, messages are available locally and there are no local overrides, so this is not a translatewiki.net issue.
What's wrong exactly?
non is not even enabled here and there's no translation, isn't it the normal behaviour for the extension to look for
non strings and fallback to English? (I don't remember.)
It shouldn't fallback to English, there is no reason why other languages should be presented in English rather than the local wiki language.
Well, the user language information are in the language they refer to because they're supposed to be useful to people speaking that language (so French proficiency information is always in French, and so on); the local wiki language doesn't matter at all. This is only my uneducated opinion, though.
The box should be using Old Norse (
non) texts, which is only possible, if the language is available. In translatewiki.net. However, we cannot even translate to Old Norse, so there is no chance to have those texts.
For all languages that are not enabled as target languages to be translated to, we have he problem that Extension:Babel cannot be fed the needed texts. We can use the traditional template way, though, on each wiki individually.
We can also add translations to the source code directly. This does not help, since MediaWiki does not load messages for languages missing from Names.php. Nevertheless, this may prove useful, since having additional translations is certainly an improvement, and maybe a way will be found someday to make them available as well.