Hi, I’m one of the admins for the Finnish (‘fi’) translation. There’s been quite a lot of debate (again) on our own mailing list about whether we should switch to using a longer language code (‘fi_FI’) since some people consider it more ‘standard’ than the short version. Personally I don’t see much benefit and can imagine a lot of trouble for regular users in upgrading, plugin translations etc., if we were to make a switch. I could be wrong though… At the moment the only real problem is that some plugins such as WPML and Codestyling Localization assume the longer version.
Since the Codex seems to recommend using the long form (http://codex.wordpress.org/Translating_WordPress#Repository_File_Structure), I’m wondering what others’ opinions are on this. Have other locales made such a transition successfully?