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Ok, so a medium-sized resort with lots of telecabins. I would personally (recovered, vaccinated, soon to be boostered) just wear a thin buff type covering which is what I normally ski in. I wouldn't expect to be stopped and asked to change for a medical mask. But I don't have the pressure of not being allowed to fly if I test positive. If you'd like some actual protection, I stick with my suggestion of carrying a medical mask and just putting that on when heading inside.
I think the UK will accept certificates in French but you should double check. I would suggest having your vaccination certificate on an app as you'll need it to get in to any restaurant and most places are set up to just scan a QR code rather than read a physical form. If you can transfer it to the Swiss Covid Cert or French equivalent app then even better.
Where in Switzerland? Generally you'll need to book your test at least two days before, maybe earlier if there's only one place in the town offering them, availability isn't super high. In general it isn't too much hassle, but make sure you check what languages are available for the certificate and what languages are accepted on return! I don't think UK will accept test certificates in German. If you have more specific questions, then I'd be happy to help.