From Fedora Project Wiki
Please integrate in the system some "language" info so apps know what language the user is typing. They need this info to select automatically the right spellchecker and OpenType rules.
Since there is no 1:1 relationship between languages and input methods (the same method can be used to input different languages, and different methods can be used to input the same language) both input and language info are needed.
(this is one thing Windows i18n gets right and Linux get totally wrong)