I learned English from e.g. the Monkey Island games.

Arrrr!

Games serve as engaging tools for English learning, promoting vocabulary acquisition, grammar comprehension, and language fluency while making the learning process enjoyable

Although not a game specifically, if you (or whomever the games may be for) want to take the learning slowly, perhaps JRPGs and visual novels might be a better pick, as the player usually needs to confirm when he/she wants to proceed to the next line in conversations, and they're usually centered around plot, which could be another motivation to try to learn. Maybe games with plenty of comedy might be good too, since understanding the joke often requires understanding the language it is told through, and I imagine it could possibly either help teach more of such, or incentivize the player to go after more information.

If they were in GOG, Civilization and Civilization II would be great for that. Descriptions of wonders and inventions would add a lot of useful vocabulary. Then also King of Dragon Pass :)

https://www.gog.com/en/game/king_of_dragon_pass

since Six Ages: Ride like the Wind is the loose sequel.

Good games and a great game world (Glorantha).

In some Yakuza games (unfortunately not in entire series) you can pause a cutscene and read subtitles calmfully.

Thank you Mr AI. Now could you please finish my home assignment about WWII? About 1000 words, please.

I learned English also from e.g. Rambo and other Vietnam war movies, which is why my English teacher wondered how come I know so many military and war terms, like POW, KIA, MIA etc. My teacher didn't even know what KIA and MIA mean and had to look it up, ha! I totally humiliated him!

Picked up quite a bit of English from imported games back when. None of them adventure games. Mainly strategy games actually. Back when Germany's USK was extremely ban-happy I started buying imports to avoid stupid self-censored versions that were released for the German market, but I kept buying original English language games afterwards also to avoid questionable German translations/dubs. Starcraft, C&C: Red Alert, Master of Orion 2, Diablo...

It did give the English I learned in school a bit of a boost when I moved to the States, but it took quite an adjustment still at the time.

My best english teachers were the AVGN and SponnyOne :)

Oh, well, and before that it was Cartoon Network in English on German satelite TV!