Request to Support RFC 5646 (BCP 47) Format for Localized Property

[willysoft]

Is there an existing issue for this?

• I have searched the existing issues

Describe the problem to be solved

Currently, the Localized property only supports ISO 639-1 format, which limits the ability to support different language regions (e.g., zh-TW and zh-CN) simultaneously. Navigator.language returns values in the RFC 5646 (BCP 47) format, which allows more specific language and regional tags. This discrepancy prevents a flexible localization setup that can support multiple variants of the same language, such as zh-TW (Traditional Chinese) and zh-CN (Simplified Chinese), which is important for applications targeting users in both Taiwan and Mainland China.

Suggest a solution

It would be great to extend the Localized property to support RFC 5646 (BCP 47) format, allowing it to handle language tags like zh-TW, zh-CN, and others that specify both language and region. This would enable better compatibility with modern browser behavior and allow localization to be more precise.

Additional context

• Navigator.language and most modern web APIs return language tags in RFC 5646 format, which is more flexible than the ISO 639-1 standard.
• Supporting RFC 5646 would also allow applications to serve different content based on both language and regional preferences, ensuring a more tailored user experience.

Key Code Section
The relevant code is located in ./l10n/l10n.js, which handles localization settings and language properties. Adjusting this logic to support RFC 5646 (BCP 47) format should allow multiple language variants to be used simultaneously.

[tarampampam]

Could you please make a PR with all the required changes? The feature sounds good to me