Your even listener is definitely on the right track, and I have a feeling it's working on some of your links and not others. Anything that already rendered on the page won't be updated, but new calls to route() after that change should have the correct default, e.g. if you navigate to another page in the app or trigger a re-render somehow.

For stuff like this, particularly with locales since all your links will change, I would suggest forcing a full page reload on the one request where the locale is changed. The alternative would be a combination of what you're doing now and also refactoring to ensure that every place you're using route() re-renders after the locale changes, either with computed() or something else.