The only problem with people speaking in online games is that people often use a lot of slang and shorten words for faster typing ("text speak"), so you might be learning poor English. Then there is the fact that most of them can't spell or type. That being said, there's a game I was playing a lot of recently called Magic Rush: Heroes. It's a phone/tablet game. People from all over the world play it, and the game has a built-in translator. There are English-speaking clans on there, and if you join an active clan, there will be a lot of conversation in the clan chat. I joined a Filipino clan and learnt some Tagalog, as well as some Russian in a Russian clan.