Is it permissible to give my writings to a foreign young man who proselytizes Christianity, so that he may teach the Arabic language to foreigners with them, knowing that there are fears of him exploiting their learning of Arabic for proselytization?

If you suspect that a Christian is working to Christianize Muslims, then it is forbidden for you to assist him, based on the Almighty's saying: "And do not cooperate in sin and aggression." You must inform the authorities and warn people about him. Whoever assists him while knowing [his intentions] has committed one of the nullifiers of Islam, based on the Almighty's saying: "And whoever among you takes them as allies, indeed, he is one of them. Indeed, Allah does not guide the wrongdoing people."