Please change the directory name of the directory used to store the Norwegian Bokmål translation from nb_NO to nb. This will make it consistent with the other packages translated to Norwegian Bokmål, and ease the work of the Norwegian translators.
Now the translation files are stored in locale/nb_NO/LC_MESSAGES/squirrelmail.{mo|po}, but in the future they should be stored in locale/nb/LC_MESSAGES/squirrelmail.{mo|po}.
As you can see from the links below most translations store their messages in nb, and only a select few use nb_NO.
http://www.debian.org/international/l10n/po/nb http://www.debian.org/international/l10n/po/nb_NO
I see you already do this with the language code 'ar', so this shouldn't be much of a problem.
Altough I'm not the maintainer of Norwegian Nynorsk (nn_NO), I know they've asked for the same fix. As you can see, the same "problem" is located there too.
http://www.debian.org/international/l10n/po/nn http://www.debian.org/international/l10n/po/nn_NO
CC to i18n-no@ since the request came from them. Please keep them included in the conversation.
Regards, Robin Smidsrød