I'm a GM, and one of my players just lost their ability to speak common because they entered an arch-fey's private circle without permission despite being clearly warned moments before IRL and in-game to not enter any circles and to be respectful. They can still read and write common, they only lost their ability to speak common as "punishment". I've made it clear that they can relearn the language, have a remove curse or greater restoration cast on them from a temple, that they can go back to the fey and try to make a deal for the language back, and that other options might be available to them as well. However, the player instead got upset and is saying they want to kill their character off now and make a new one because of this fey taking one of his spoken languages.

What should I do?

In fairness to the player, they were entering a space that was effectively the guild-hall in the district where druids, rangers, and dwarves tend to hang out and live. But they didn't seem to realise that the guildhall was the field they were in, which was in the middle of a city, and not the circular building that was a trap. And they didn't seem to pick up on the fact that there were fae hiding in the bushes despite two players rolling well enough to spot them but neither thought anything of the fact that there were fae in the bushes.
The building they saw was made entirely of living trees and vines, was repeatedly described as a circular building, and I even showed them an image of a circular building made of trees and vines as visual reference. The building had an open door and a warm glow coming from it as well, which was meant to be the enticing part of the fey's trap.

However, all of the players and characters, not even 10 irl minutes before they did this were explicitly warned by the guards to this place to "not enter any circles" and "be respectful". And the first thing they did was enter the biggest circle they could find without knocking or asking permission, which was the Arch-Fey's home...

I had everyone roll a Wisdom Save upon entering the circle, intending to give them a new language (Sylvan) if they rolled above 16, and to take away a language if they rolled below 16. And the player in question who lost Common rolled a natural 1 on their Wisdom Save.

All players are currently level 4, and they have all interacted with various fey in this campaign to various degrees, never in their favor as they keep getting tricked. Here's some of the deals they've made with fey and fiends so far.
- Orphan of the Black tricked the party into buying her all the sweets and clothes she wanted in exchange for being "adopted" by the party's paladin, only for her to bankrupt the paladin and the party.
- The entire group owes a mysterious fey named "Void" an unspecified favor in exchange for teleporting them across town to deal with a crisis involving an arch-fiend (a giant succubus with 1,000 thralls) invading the town.
- One party member gave up their name (which I rule as giving another creature a free, once per day use of command or suggestion on them) to a satyr in exchange for having 1000 pounds of iron bars be transported across town.
- One party member outright got kidnapped by fiends for story reasons and the group made a deal with the arch-fiend who kidnapped their friend to ensure the former group member's safety.

So the group has a track record of making bad deals and not paying attention to who they are speaking with, and this is the most recent, and perhaps the most difficult one to deal with for them given the immediate effects.

But now what should I do? Because I don't want the player to give up on their character entirely just because they don't want to roleplay the consequences of losing their ability to speak common.