Default Language chosen by domain?

I know that there is some level of browser language detection, but I’m wondering if there’s a safe way to set the default language based on the domain used.

e.g., the instance is, but users might visit - be forwarded to the base English instance but now the default language of the UI is Welsh.

I’m working on a bi-lingual English Welsh instance, and I’d like the preference to be visible through the domain, as well as allowing the individual user to then set their preferred language.

(Yes, I know there’s no Welsh translation yet, that will be the next thing after figuring this one out :o)