Most movies do this if they want the viewer to understand who the main characters are because ultimately the POV of the film is that of the Natives. Not the French or the Predator, so when the scene only had Natives in it we got the language barrier removed.
Warrior (TV Show on HBO Max) does this as well. Main story is about Chinese immigrants, so when the scenes only contain those characters the dialogue is modern American English. When the other characters are in the scenes (Irish or Anglo-Saxons) the Chinese characters speak Cantonese or their English is accented.
For Prey the only thing about them doing it that was kind of annoying is when they'd mix Comanche in with the English of the Natives. I also didn't like that the French dialogue was subtitled in French, if you want us to feel like the Natives and not understand their language that's fine...but don't add the subtitles in unless they are to show us what's being said.