2009/9/9 Tisza Gergő gtisza@gmail.com:
The LanguageSelector extension [1] can automatically set the interface language based on browser settings, which is nowadays the norm for every serious multilanguage web page. It is not used on WMF wikis, because it would interfere with caching.
I'm not convinced using the browser language settings for anything other than suggestions is a good practice, as it doesn't necessarily relate at all to language speaking ability of the user behind the browser (think Internet cafes, shared computers, etc.). I notice that it's possible to disable this behavior in the extension and just use it as a UI language picker, which I agree would be useful if we can make it work efficiently.
IMO an approach that replicates the behavior of separate MediaWiki instances on a per-page basis, i.e. where the UI language reflects the content language _of the page_, may be worth considering as well. Then, if you navigate through an entry point in your language, and peruse pages in your language, your UI will be in your language as well, consistently.