Translation (language) settings do not stick

Hello.

If <debian.org> correctly defaults to Japanese, but English is manually  
selected, that manual selection is reverted upon following any link.   
Here is a demonstration:

https://i.imgur.com/zbtyHLJ.gif

This can be very frustrating.  The issue is reproducible using Firefox  
ESR 68 and Chromium 78.  Thank you for listening.