html lang attribute gets only set dynamically

[slatian]

Summary

The lang attribute on the html tag only gets set through javascript while it should already be set correctly when the page gets delivered.

Compare the html code that shows up in the inspector with javacript enabled and with javascript disabled (here the language tag ).

Seems to be similar in observed behavior to #2960 from three years ago.

URL

• https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Global_Objects/decodeURIComponent
• https://developer.mozilla.org/ja/docs/Web/API/HIDDevice/forget

But it should be the same issue on all non-english pages.

Reproduction steps

1. Disable javacript or fetch the page using curl
2. Look at the html lang attribute

Expected behavior

The html lang attribute matches the document language (like it does when javascript is enabled).

Actual behavior

The attribute always says en-US regardless of language.

Device

Desktop

Browser

Firefox

Browser version

Stable

Operating system

Linux

Screenshot

No response

Anything else?

No response

Validations

• I have read the Community Participation Guidelines.
• I have verified that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• I have checked that this is a concrete bug. For Q&A open a GitHub Discussion.