Navigating to a page which is configured to redirect elsewhere results in a 404 if the user's browser isn't in English

[globau]

Summary What is the problem?

Navigating to a page which is configured to redirect elsewhere results in a 404 if the user's browser isn't in English.

Steps To Reproduce (STR) How can we reproduce the problem?

1. Change your web browser to Spanish
2. Visit https://developer.mozilla.org/docs/Mozilla/QA/Bug_writing_guidelines

Actual behavior What actually happened?

Redirected to https://developer.mozilla.org/LN/docs/Mozilla/QA/Bug_writing_guidelines which is a 404

Expected behavior What did you expect to happen?

Redirected to https://bugzilla.mozilla.org/page.cgi?id=bug-writing.html as per https://github.com/mdn/content/blob/main/files/en-us/_redirects.txt

Additional context Is there anything else we should know?

Originally filed by CarlosT as https://bugzilla.mozilla.org/show_bug.cgi?id=1740704