One of disadvantages of Redmine is that when a not supported language is used it shows “translation missing: xx,...”. That is, for example, when a user uses “xx” language and it’s not supported he/she sees... nothing! That is not even English!.. Not good!
What I think about is to: a) fall back to English and b) convert it to a link allowing to specify translation for “xx” language. Some plugin existes for the a)... and I believe b) is possible...
This can (and should) be used for translating the whole Redmine...