Snolus: It does list French and Russian as languages for the interface on the Steam page, but not on GOG. Now I don't know anything about GOG's internal shenanigans when it comes to that - if you own the game on GOG, would you mind checking whether those languages are available?
King Arthur's Gold added for missing DLC (for now)
SCPM: It has French, Italian, Russian, Polish, and Spanish as available languages in game.
Also, the note for the Steam DLC in game says: "Currently only available through steam as a DLC. If there's enough interest we can investigate non-steam options."
The Patreon stuff includes "heads packs, priority server access, discord rewards, fancy capes, and even custom heads", based on the different monthly pledge tiers.
Additionally, the game will eventually be transitioning to F2P, see here:
https://www.patreon.com/kingarthursgold This sounds like an unholy rabbit's hole. Will need to add all of these bits later today.