An user from the nowiki added labels and got "no" as language code , as in this edit. When I checked this I found that both "nb" and "no" are in the list on Special:Preferences#mw-prefsection-personal as "norsk bokmål". The language code "no" is a macrocode for both Norwegian Bokmål and Norwegian Nynorsk. The code "nb" is the content code we are using at nowiki.

I have asked the user Asav if he has selected the "no" language code in preferences. An other possible cause can be that he has "no" in the Babel boxes, will this create an entry for "no" in the signature section? A third possible cause is that there might be a gadget involved.

Seems like it is the Babel-box that created the problem in this case.
Confirmed, it was the Babel-code.