There is a pitch up for adding support for Swift to Cloud Functions to Firebase. Given Swift's great properties for serverless functions compared to some of the traditional languages currently used. If you would be interested in seeing this supported, you can vote here
It would be great to see this added
Disclosure note: I'm not affiliated with Google or Firebase in anyway, I just think it would be great to have Swift as a supported language here
We use Firebase at work, and I’m very pleased with the platform.
Being able to write Firebase Functions in Swift would be an incredible productivity boost compared to our current Typescript code.
Unfortunately I can’t vote for this as I am the OP of the request. 
But others: please follow the suggestion and vote. The Firebase team is awesome and they do use the votes for prioritization.
Voted! Would also love to see Swift for Supabase edge functions. Anyone know the people to make that happen?