Only offer translation for supported languages (#23879)

.rubocop.yml

app/javascript/mastodon/components/status_content.jsx

app/javascript/mastodon/initial_state.js

app/lib/translation_service.rb

app/lib/translation_service/deepl.rb

app/lib/translation_service/libre_translate.rb

app/models/status.rb

app/serializers/initial_state_serializer.rb

app/serializers/rest/status_serializer.rb

app/services/translate_status_service.rb

spec/lib/translation_service/deepl_spec.rb

spec/lib/translation_service/libre_translate_spec.rb

spec/models/status_spec.rb