I installed i18n module to enable my site support multilanguage contents.
Is it important of the folder name of each language ?
e.g.
my site is on /default folder
I will create four languages, English, Chinese Simplified, Chinese Traditional and Japanese
Each language folder I created will be

/default/eng for English
/default/chs for Chinese Simplified
/default/cht for Chinese Traditional
/default/jpn for Japanese

or the each language folder name should match the language code defined in includes/locale.inc i.e. the folder name should be

/default/en for English
/default/zh-hans for Chinese Simplified
/default/zh-hant for Chinese Traditional
/default/ja for Japanese