Current stable has the translations in a different
package, and even separate packages for each language.
So it's very well possible that not all (or even none)
of the languages are available.
By default SquirrelMail doesn't cope with this. As a
user you're still presented with all possible languages
in the Options - Display Preferences screen even when
some of them are known to not work.
How to deal with this? Some suggestions:
a) Somehow detect this from conf.pl and build the list
there. Advantage: efficient; disadvantage: list is not
b) In options - display preferences: do an file_exists
for each language and display only those whose dir is
present. When none present, show only English or no
selection possibilities at all.
c) Same as (b), but on login. I think (b) is more
efficient since users will log in more than they will
access their options pages.
An alternative to the file_exists can also be to do a
dirlisting of locale/ and match the resultst against
our list of languages; that would be a bit more
efficient I guess.