Do you change your name when you speak a different language? Why would a web site?
But I think that you could make a theme component that would do that with some ease. If any of thousands of people using Discourse had needed that (and also thought it was armature) absurd) not to change the title when locale changed there would be a mature theme component already in available. But now you’ve found your place to contribute. Depending on how many things you want to customize for each locale, I’d guess it’s $250 to $1000 of work (which you can do yourself if you have the skills and desire).