So, I went through my old saves, and found one I liked but was still set back in vanilla. Now, I'm fine playing vanilla, but I already have two good runs there, so I opted to add the Royalty DLC to this one. I've also opted to put Rim Languages in all my runs, so how does it react in this situation?

Well then..

This mod's description states:

Removing and adding fractions in midgame: This will most likely lead to a collapse, do not add or remove factions from your save..

I have backup files, so this is not a problem here. .

After adding the Empire faction that comes with Royalty (I had to do this manual, because the game does not appear to do so - at least not for modded saves) the mod does not appear to check for them to add a language. The other languages are unscathed.

Other than the mod not generating a languages for the added faction, it does not appear to have broken anything. There are no persistent errors.

In order to award the new faction a language, we must:

1. Remove Rim Lang: This will removes all languages. Save and exit.
2. Reinstall RimLang: Re-instate RimLang. This will add new languages for all faction. There are no reported errors, but we do lose previous learning progress.

Even though this does not appear to have caused any lasting damage, it might be better to go with the safer approach:

1. Remove RimLang from the save file first.
2. Add the new faction.
3. Reinstate RimLang to award languages again.

The result is the same for either case, however. All languages start from scratch.