Wikimedia Bugzilla is closed!

Apologies upfront for this bug report being rather unspecific, but I cannot pinpoint the source of the trouble. I can only describe the symptoms.

0. The Commons uses a Javascript-enhanced upload form with extra fields and extra labels. Users who visit the upload form and have their user interface language set to a language for which the Commons has no translations yet are shown the English labels, plus a link saying "translate" in their language, which, when clicked, takes them to the page [[:commons:MediaWiki talk:UploadFormLabels/UploadFormTranslations]]. They can then enter their translations of the labels there, and once they're installed (copied to the right messages in MediaWiki-space), the upload form has the labels for this language. This all has worked perfectly fine since the new upload form had been introduced back in May 2008.

1. Since around Christmas 2008 or shortly afterwards, the page http://commons.wikimedia.org/wiki/MediaWiki_talk:UploadFormLabels/UploadFormTranslations is getting a lot of traffic with translations for languages for which there are already translated labels (es, de, fr, ...). This indicates that many people apparently don't see the already translated labels, but get the English labels plus the "translate" link.

2. This is corroborated by a report by a Czech user. See http://commons.wikimedia.org/w/index.php?title=MediaWiki_talk:UploadFormLabels/UploadFormTranslations&oldid=17377370#New_translations_by_User:Slfi
The user reports that he sees English labels on the Upload page (his user interface language is Czech). At the same time, I can see the same upload form using the same links (and also setting my user interface language to Czech) completely in Czech language.

3. On the Finnish (Suomi) upload forms, a slightly different problem occurs: visiting  the upload forms for "ownwork" or "fromflick" uploads (using the "uselang=fiownwork" hack that the Commons has employed since way back), the page is served with the interface in English, even though the form shows up in Suomi allright -- for me; but apparently again not for others; see http://commons.wikimedia.org/w/index.php?title=MediaWiki_talk:UploadFormLabels/UploadFormTranslations&oldid=17377370#New_translations_by_User:Apalsola
The source indicates wgUserLanguage="fiownwork", wgContentLanguage="en". By contrast, the page http://commons.wikimedia.org/w/index.php?title=Special:Upload&uselang=fi is served with the interface in Suomi.

Questions:
a) Has there been any server-side source code change related to the handling of user interface languages or the uselang parameter?
b) Has there been any change (maybe a configuration somewhere?) concerning the uselang hacks (XXownwork, XXfromflickr, and so on)?
c) Could this be some strange caching issue, in which I just happen to get the "right" versions from one cache server, while others get wrongly cached or outdated versions from other cache servers? (Note: the behavior on my side is the same if I force a complete reload in Firefox)
d) Might this have something to do with the server relocation in Amsterdam? I note that all these problems concern European languages. So far I have not seen any similar reports about Asian languages.