Internationalization: Clarify fallback

[erosman]

MDN URL

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization

What specific section or headline is this issue about?

Localized string selection

What information was incorrect, unhelpful, or incomplete?

The explanation and examples on MDN don’t appear to clarify the following scenario.

• _locales/en/messages.json (extension default)

{
  "colorLocalized": { "message": "colour" },
  "time": { "message": "Time" }
}

• _locales/fr/messages.json

{
  "colorLocalized": { "message": "couleur" },
  "time": { "message": "Temps" }
}

• _locales/fr_BE/messages.json (browser locale)

{
  "colorLocalized": { "message": "couleur" }
}

What would browser.i18n.getMessage('time') show, "Temps" or "Time"?

What did you expect to see?

Improved explanation

Do you have any supporting links, references, or citations?

No response

Do you have anything more you want to share?

No response

MDN metadata

Page report details

• Folder: en-us/mozilla/add-ons/webextensions/internationalization
• MDN URL: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/mozilla/add-ons/webextensions/internationalization/index.md
• Last commit: 32fb8af
• Document last modified: 2025-10-25T08:22:15.000Z

[rebloor]

@erosman this is covered under https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization#localized_string_selection, more specifically:

if the browser locale is qualified with a script or region (e.g., en-US or zh-Hans-CN) and there is a messages.json file for the regionless version and failing that the scriptless version of that locale and that file contains the string, return it. For example, if the user has set their browser to zh-Hans-CN (and there is no _locales/zh_Hans_CN/messages.json file) the i18n system looks for a string in zh-Hans, and if that isn't available, zh.

I guess your question is "What would browser.i18n.getMessage('time') show" if the browsers locale is set to fr_BE. Then the answer would be "Temps"

[erosman]

, if the user has set their browser to zh-Hans-CN (and there is no _locales/zh_Hans_CN/messages.json file) the i18n system looks for a string in zh-Hans, and if that isn't available, zh.

@rebloor The explanation shows that local is switched from zh-Hans-CN to zh-Hans if the file does not exist.
That is not the case in my example.
The file does exist. However, the property does not exist in that file.

MDN only explains the process with missing file, not missing property.

[rebloor]

@erosman thatnks for the clarification - I'll check and update.