Right now, since fof/linguist isn’t yet updated for Flarum 2.x, the best workaround is to manually edit the language files in your locale folder. You can copy the existing 1.x Swedish language pack, adjust any outdated or missing keys by comparing it with the default English en.yml in vendor/flarum/, and then place your updated .yml file under extensions/your-lang/locale/.
It’s also a good idea to follow the FoF Linguist GitHub repo for progress on 2.x support — once it’s updated, you’ll be able to manage translations directly from the admin interface again.