According to the manual, the LANG authorized value ships with Koha. However, there are no values for the category. The description says it should have ISO 639-2 standard language codes. If a library adds the LANG authorized value to a tag subfield, such as the 041$a, they have no options available.
What do you mean with "they have no options available"?
The authorized value category is there, but has no values. If a user adds the LANG authorized value category to a framework tag subfield and then tries to use the drop down in the basic editor, there are no values. A user would expect there to be values since the category is included in a default installation.
Hm, I think I remember that we added the category because it's used in UNIMARC frameworks. But I am not sure if there is a full list somewhere. The only thing I'd dread a little is having to translate language names a third time.... (XSLT, installer and staff interface all have separate po files...).