If you downloaded Amethyst from Play Store it has access to a auto-translate functionality.

It translate the notes as you read them, for optimization, it only has the "dictionary" of the languages detected, when a new language is found it'll download the zip file needed to translate it, if you check quickly the notification you'll see the language code as the zip filename.

Nothing to be worried about, but if you prefer not to have this behavior you can just download it from other sources like from F-Droid.

You can check all the download sources from here: https://github.com/vitorpamplona/amethyst