If they go forward with this, for the entire movie all of Gambit's dialogue should be subtitled and none of it audibly intelligible. All characters interacting with Gambit should understand him clearly except for one secondary character that can't NEVER understand Gambit is saying and this character doesn't understand how everyone else can understand Gambit so clearly all the time.
I think you are forgetting that this was a deadpool movie, so every character feels light hearted. In an actual movie with real story, I think Tatum would nail it.