Mac storage basics · User accounts, voices and system extras
How do I remove downloaded translation languages on a Mac?
Short answer: Open System Settings → General → Language & Region → Translation Languages and remove the languages you don't need; they can be downloaded again later.
Languages you've downloaded for on-device translation are listed in System Settings → General → Language & Region → Translation Languages…. Remove the ones you don't need there.
Translation still works for removed languages when you're online, or you can download them again later. This is separate from the languages apps include for their menus — see removing app languages.