Switch language once, don't switch back to headers
Usually browsers send preferred language headers, and spitting out the right page on first contact through Accept-Language is cool, but if a user explicitly clicks on a different supported language, that one must show up on subsequent page-loads.
I.e.: I set my browser to send: Accept-Language: es;q=0.8,fr;q=0.5,en;q=0.3
I get a nice redirect to https://demo.bitmask.net/es, where I click on the English (/en). I arrive on the English page, when I now do anything (register, create account, read privacy notice...) I will again end up on the /es/ page. Expected behavior: after a user manually choses a specific language, they won't be auto-redirected to a page in another language anymore.