The recommended code for `_middleware.ts` does not work in prod, but does work locally.  You need to use `request.nextUrl.pathname` to properly redirect from what I can tell.  You also need to have a quick helper function to strip off the `/default` locale at the start of the pathname as we are providing `/en` as a fallback locale.

FWIW - I am pretty new to NextJS.  Someone with more experience should probably review this suggestion before merging it.  What I can tell you however is that the code as it is in `_middleware.ts` works locally but breaks in prod.  To test this out use the code and navigate to `https//www.mysite.com` - it will work as expected on the root url, as this matches `nextUrl.href`.  Now try navigating to `https//www.mysite.com/about` and you will be redirected to `https://www.mysite.com/en/https://www.mysite.com/about`.