Last modified: 2014-07-08 16:29:38 UTC
Navigators send a list of acceptable languages (English, French etc.) by decreasing preferences. By default, MediaWiki on commons and other multilingual sites should default to the first language that it knows in that list. (Francophone users have complained that the commons user interface is in English even though they follow links from fr:)
Neither the translansatios or the message choosing algorithm is able to provide pleasent user experience, yet. Not at least for non-major languages.
I'm going ahead and reopening this. Something 'in the middle' such as a runtime JS check could switch (or prompt you with the ability to switch) the UI language fairly straightforwardly with today's interface. A future more JS-heavy interface might be more able to dynamically switch itself transparently.
When not just give the user an option in a small prompt per his browser language preferences?