New user accounts on Wikimedia Commons automatically get a greeting from [[User:Wikimedia Commons Welcome]]. However, this greeting is in English and not all users speak English. At the top of the message there is a list of links to translations in other languages, but I think there is a better way.
Since most new user accounts on Commons (about two thirds) are created by SUL, and arrive through a link that specifies the uselang= parameter, wouldn't it be very easy to set the user preference for user interface language from the uselang parameter when the account is created by SUL?
The greeting template (and other templates, such as deletion requests) could then access the user's interface language setting through a {{USELANG}} magic word, and present the corresponding translation.
This way, new Swedish speaking users (who typically arrive from the Swedish Wikipedia, one that doesn't allow local uploads) could be guided to the Swedish language village pump and find a community there.