luci-i18n: adding languages to the system prevents English in auto mode

[pmelange]

Is there an existing issue for this?

• I have searched among all existing issues (including closed issues)

screenshots or captures

Tested with 25.12.5

Setup:

• Browser: set your default display language to English, and add German as a secondary display language. Loaded websites should prefer English
• Firmware: Build an image on firmware-selector. customize it by adding the package luci-i18n-base-de.

Upon going to LuCI, the text will be in German, even though English has a higher priority in the display list in the browser. It is possible to force English in LuCI under the "Language and Style" setting. But auto will not display English.

Workaround:

• Leave the LuCI setting in "Language and Style" to "auto".
• run uci set luci.languages.en='English'; uci commit luci
• Now the browser will show whichever language has the highest priority in the display settings.

Proposal:
Since English is installed by default, add the option to luci.languages

Background:
The environment where this was detected is in a community network firmware which supports multiple languages on the web interface. Some users prefer to have an English interface even though their primary language is a another one. Or even, some users have English as their primary language, but can get by when necessary with a second language. As the community network firmware has publicly available status pages, the users don't have the ability to modify the LuCI settings. The users ended up setting to only display English while accessing the firmware status page, then setting it back to multiple languages once done. This was the first bread crumb on this journey.

Actual behaviour

Setup:

• Browser: set your default display language to English, and add German as a secondary display language. Loaded websites should prefer English
• Firmware: Build an image on firmware-selector. customize it by adding the package luci-i18n-base-de.

Upon going to LuCI, the text will be in German, even though English has a higher priority in the display list in the browser. It is possible to force English in LuCI under the "Language and Style" setting. But auto will not display English.

Expected behaviour

Seeing English if English is higher in the browser's language display list.

Steps to reproduce

Setup:

• Browser: set your default display language to English, and add German as a secondary display language. Loaded websites should prefer English
• Firmware: Build an image on firmware-selector. customize it by adding the package luci-i18n-base-de.

Upon going to LuCI, the text will be in German, even though English has a higher priority in the display list in the browser. It is possible to force English in LuCI under the "Language and Style" setting. But auto will not display English.

Additional Information

{
	"kernel": "6.12.94",
	"hostname": "OpenWrt",
	"system": "e500v2",
	"model": "TP-Link TL-WDR4900 v1",
	"board_name": "tplink,tl-wdr4900-v1",
	"rootfs_type": "squashfs",
	"release": {
		"distribution": "OpenWrt",
		"version": "25.12.5",
		"firmware_url": "https://downloads.openwrt.org/",
		"revision": "r33051-f5dae5ece4",
		"target": "mpc85xx/p1010",
		"description": "OpenWrt 25.12.5 r33051-f5dae5ece4",
		"builddate": "1782737960"
	}
}

What browsers do you see the problem on?

Firefox, Chrome

Relevant log output