I've implemented what's being currently requested in the above patch, however let's be sure we understand all the details:
- On local wikis, it makes sense to use wiki language
- On Commons, the default language is English - however the whole wiki makes this almost transparent, using user's UI language as fully as possible. Does it make sense to use user language on Commons?
There is one possible pitfall of doing that. Commons file page UI does not make it very clear when you are viewing a file in a given language versus when you are viewing a file that has been switch translated into a given language. If we start to show images by default in user's language, we might make that problem worse by tricking people into thinking that the file is only available for the language they see it in. They might go ahead and embed it in wikis where that's not the default language (maybe a variant/closely related language) and the file will end up with English labels on that wiki.
Hence, I think it's best if we let the default language for files on Commons remain English.