When a student opens a test, the buttons, menus and instructions around it now appear in the test's own language by default — so a Dutch test comes with a Dutch interface, and an English test with an English one.
Until now that surrounding interface followed the browser's language, which meant a Dutch test could open with English controls for a student whose browser was set to English. Now it takes its cue from the test itself.
Anyone can still switch languages from the Language menu, and a saved preference always wins — so this only changes the starting point, it never takes the choice away.