How can money illegally taken from a mixed foreign company be returned, given that the direct manager facilitated this, and is this money considered an injustice, and does it become permissible if the manager is accountable to the company, and what is the ruling on donating a portion of it to the poor?

You must sincerely repent to Allah Almighty for your betrayal of what you were entrusted with. The conditions for repentance are: remorse, desisting from the sin, and resolving not to return to it.

Regarding the money, you must immediately return what you took to the company's treasury. It is not sufficient for you to give it as charity or to hand it over to the manager if you know he will misuse it.

As for the manager, he must be advised and rebuked. If he does not desist, then report him to his superior, unless you fear a greater harm.