The refresh token plugin config was removed in MDL-78750:

Generating a refresh token (which we currently have as a required field) triggers a short expiry time for the access token (5 mins by default). We are also not using that token to refresh access, so it's essentially just making this impractical to use. We should therefore just remove the refresh token setting altogether.

The language strings were left over, we should deprecate them. Found while looking at MDL-79373