Here you can make new language file, correct existing one, or translate only new version's labels (marked in red). The modifications are not automatic. You have to download and copy generated file to your KCFinder's lang directory. To get KCFinder to work with your language, you should to set lang GET parameter pointed to your language code (e.g. browse.php?lang=de). Possible formats for the language code are:
If you want to include your new or modified language file into the official package, you should to post new topic here or send me an e-mail (located in each source file).