@Tutanota Yep, more likely they haven't explored that feature. Or, they are using a fediverse software and/or app that doesn't have language filters; or doesn't use their account's language filter settings.

In any case, it's going to be a challenge. For one, you're in the mastodon.social instance which is limited to 500 characters. If multiple languages in one post will be your chosen strategy, you may have to transfer to a different instance with 1,000 or even 2,000-character limit.

Or, maybe just post in English, since your reach and market is global.

Another option is, keep separate accounts. You can take advantage of mastodon.social's twin server, mastodon.online. ;)