Yup .. copy the english locales to finnish.
cp [PLUGINPATH]/config/locales/client.en.yml [PLUGINPATH]/config/locales/client.fi.yml
cp [PLUGINPATH]/config/locales/server.en.yml [PLUGINPATH]/config/locales/server.fi.yml
You need to enter your web container if you’re using docker and go to /var/www/discourse/plugins/discourse-tagging/ (that’s your pluginpath).
After you do this, you need to restart the docker (maybe rebuild it even)
If you have a manual setup, you have to figure out on your own where your ruby files are located