Zaba has a good point, IMO the club has to make players learn English. Being comfortable speaking in English must make them feel a million times more at home, not to mention it means they can do interviews which bonds them to the fanbase.
On top of that it must be better for marketing.
I can't believe Aguero has still not learned the language, but we should be right on top of it with Sané, Jesus and anyone who follows behind them.