Hi @alziga,
By default Magento language packs on M1 are located at:
/app/locale/
There you'll find directories like:
If you remove the desired directory and then you refresh the cache, you won't get those translation anymore.
You should check, also, if translations are not saved into the database (becasue the translation inline).
In that case you will need to connect to your database (there isn't a graphic tool out-of-the-box) and check the core_translate table and see if translations for the locale were saved there.