It’s not a good idea to argue with your opponent in their mother tongue, even if you happen to know it rather well. Pretend ignorance and force them to speak in your language or order an interpreter. This is the way to defeat them even before the game has begun. The conversation would be so painfully awkward that he would beg you to end it and let you win.
The purpose of arguing is not to arrive at the truth. You don’t care about the truth. You care about winning.
So go and win. Truth be damned.
Never argue in english with an American or British.
Never argue in hindi with an Indian.
Never argue in mandarin with a Chinese.
The way of winning is to go full tribal on your opponent.