To uninstall language-pack-fr-base just follow these instructions.
sudo apt-get remove language-pack-fr-base
This will remove just the language-pack-fr-base package itself.
sudo apt-get remove --auto-remove language-pack-fr-base
This will remove the language-pack-fr-base package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for language-pack-fr-base then this will work.
sudo apt-get purge language-pack-fr-base
Or similarly, like this language-pack-fr-base
sudo apt-get purge --auto-remove language-pack-fr-base
|Maintainer||Language pack maintainers <email@example.com>|
|Description||translations for language French|