Don't fiddle with $wgLanguageCode in KkConverter

This was causing problems with the setlang= and uselang= parameters in the
URL being ignored on kkwiki.

Bug: 64440
Change-Id: I4e2a20c707fd4b9b8a581a9d14e04b6cfc8b4b5c
Merge "Don't fiddle with $wgLanguageCode in KkConverter"