Why do I need to re-install Thunderbird in order to change language?
Why doesn't Thunderbird / Firefox use language files? Having to un-install and then install a new version seems a bit old fashion. And it makes me unsure if I delete other settings and plugins as well. I don't want to reconfigure and install all plugins over again just to change language.
ყველა პასუხი (2)
Because that is how it works. You need to download and install the language that you want. The program file is separate from your profile where your data and settings are so they should not change. It is always a good idea to make backups of your profile even if you are not messing with the program.
Did you try installing a language pack?
http://kb.mozillazine.org/Language_packs
See also: https://addons.mozilla.org/en-us/thunderbird/addon/simple-locale-switcher/