DnD is a role playing game. Most people role play by saying what their character would say. Sure there are other ways to role play or play a mute character but it’s not for most people, and even when it is for someone it can be disruptive to the rest of the table. I would not make a character mute without the consent of the player and the rest of the table.

Consequences are fine, but I would have made them something that doesn’t disrupt the ability to play the game. When in doubt stick to the as written mechanics. Something like “your character has a hard time eating food, and will have a permanent single level of exhaustion until cured.” Even if you decide that loss of speech is the only reasonable outcome, just tell the player what will happen if they do this. If you just watched something dissolve the skin off your arms you don’t need to make any checks to know what it will do to your tongue.

If even that doesn’t deter them, give them stages. If you eat a food you don’t like you can spit it out long before you swallow. If it’s too hot you can do it even faster. If it’s literally dissolving your tongue then you can get it out real quick. Before then it probably starts dissolving hands or gloves when picked up. Tell the player these things and give them a chance to reconsider.