[2023] I went back to playing Stellaris but I can't change the language and I lost all progress saved in the cloud

Steam cloud saves are visible here:

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store.steampowered.com If your saves show there but not in the game, they are probably from an older game version and not compatible with the game as it is now. You'd need to revert to that game version in the Steam Betas tab for the game to continue them.

Game language is chosen in our Launcher now, under Game Settings (as is the separate launcher language choice). The language Steam is in does not matter.