This is due to line 71 of python/auxiliar/postprocess_html.py:
browser_language_url = "/web/about/browser-language"
This file needs a new location.
At the same time, it would be very good to remove the special-casing of
offline versus online versions of the website on line 295 of the same
python script, as it just makes it harder to find problems like this one
locally.