Typing Swedish on a keitai?

Calling all the Swedes and other-than-English/Japanese typing users of keitais!

I am dreaming of a beautiful Japanese flip phone on which i can download messenger, because textning does not cover all my necessary communication. If BankID works too that would be amazing but i think i can make it work without it most days. My question is if it is possible typing åäö in a keitai, if you can somehow use an app for it or something? And can you switch between languages on the go is is it very clunky to do so?

Should i go for the smartphone flip phones, aka a ALT MIVE style folder or Samsung Galaxy folder, instead, if i want to make it work? I have heard they can work for kind-of-dumbifying your phone life cause they are slower with a smaller screen. Obv i would prefer a keitai though!

Thanks for any advice :)))