Oh, facts, logic and reason again!/sarc
There are some, here, that think it’s perfectly acceptable for the invading army to use actual mercenaries, but cry foul when the invaded country allows foreigners to become citizens and then join the military.
Of course, they rejoice, when they are captured and sentenced to death by a kangaroo court.
The French Foreign Legion is mercenaries. Mercenary armies are generally accountable under law of war, as the leadership is openly by a state actor.