Another likely influence is that you just aren't good at feeling strong emotions in the foreign language. Like a weaker side effect of how you almost always swear in your native language, however infrequently you use it. Anger is the emotion that tells you you need to be uncooperative and unreasonable, but your brain's not used to being angry in French, so you just... aren't.

I'd be curious if this would improve if you got together with a group of drinking buddies or something and try just hurling insults at each other for a couple hours.