This option should contain a language code of the editor documentation to use with TinyMCE. These codes are in ISO-639-1 format to see if your language is available check the contents of "tinymce/jscripts/tiny_mce/theme/<theme used>/docs". The default value of this option is the value specified in the "language" option or "en" for English.
Example of usage of the docs_language option:
tinyMCE.init({ ... docs_language : "sv" });