Automatic language selection not working properly

[sjaeckel]

I've just visited the homepage with Firefox and it results in non-working links since the "automatic language selection" seems not to be working properly.

All links on the index site are pointing to https://subsurface-divelog.org/None/<target> instead of e.g. https://subsurface-divelog.org/en/<target>

I've been able to reproduce by:

1. go to about:preferences
2. in the 'General' section go to 'Languages'
3. at the point 'Choose your preferred language for displaying pages' click on "Choose"
4. remove all languages
5. visit https://subsurface-divelog.org

If you don't want to modify your existing profile, you can follow https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

This problem can also be reproduced if the "preferred languages" contains only unexpected values. I've tried: "Akan", "Basque" and "Chinese". Chromium based browsers expose the same problem. They don't allow to empty the list completely, but still they can be limited to a single language that is not recognized.

[mikeller]

I can confirm that this problem exists on Firefox.

To expand on this a bit, and more of a personal bugbear when answering to support requests, in Chrome the currently used language is encoded through an URL parameter, like so https://subsurface-divelog.org/current-release/?lang=en
This isn't helpful when users are copy/pasting URLs in requests / responses, as it includes their locale setting. An improvement might be to encode the language in the HTTP header, such as through Accept-Language.