Please make the extra language support files optionally installable. I would prefer not to install language support files for languages which I don't use or need.
I've tested simply removing all but the .ICO and .lng files for the primary system language on which MP3Tag is installed, and it behaves correctly; only one language is displayed in Options ⇒ Language, and only one language target is available for tagging (Options ⇒ Advanced ⇒ ID3v2 comment language code (ISO-639-2))