Last modified: 2009-09-10 13:35:07 UTC
As documented in the BCP 47 (RFC 4646 & RFC 4647 as current) a language tag such "de", "zh-Hant", or "kk-Cyrl-KZ" are recommended. Even the casing are shuffled (["mn-Cyrl-MN" == "MN-cYRL-mn" == "mN-cYrL-Mn"] are the same code, as listed in page 5 on RFC 4646). All of the language code that requested must not case sensistive, such as http://localhost:8080/~man/mediawiki_svn/index.php/Special:Version?lang=ko-KP will show the North Korean script instead of English, which was detected as invalid code. And the language codes showing should be comply with the BCP 47 recommendations, although the language code showing in preferences are comply with the recommendation so far.
Marking this FIXED. r55022 did some cleanup for this, and I don't see the need for a tracking bug with no dependencies.