Any language checked in the available_languages option, below, can be chosen as the preferred_language. You will need to select an additional language below and then submit the change before you will be able to change the preferred_language option.
The list of languages controls which natural languages you would like your members to be able to view the list in. It would allow a user to send and receive mail with hiragana (the Japanese writing system). You must also add a language here before you can change the preferred_language option, above. Mailman cannot translate languages, this option only allows other character sets to be viewable.
If you have changed your preferred_language to a non-ASCII character set (such as hiragana), you may wish to set this to Always if you have added a subject_prefix (in the General Options) to your Mailman list. If your list can receive encoded (non-ASCII) and unencoded (ASCII), you may wish to set this to As needed.