I had a friend who learned English almost exclusively through video games including FFXIV. I think the thing is everyone is focusing on the quest text as what you would be learning from, but they spent so much time in voice chat with us that I feel that's how the learnt the most. I would recommend playing the game but also investing in voice chat (with them and several other English speakers), then while they can gain something from the text in game they also learn from you and other English speakers talking together and they can ask questions too.