ISO 639 - PHP中可靠的查找资源

Intl Extension Uses The RFC 4646 Language Tag

In the PHP intl extension, specifically the Locale class, it says:

Locales are identified using RFC 4646 language tags

RFC 4646 is deprecated

The reason I mention this is that RFC 4646 has been deprecated in favour of RFC 5646.

I had intended to use the intl extension to translate ISO 639 codes to their respective language name (e.g. en to English). Whilst this is not essential, it would be a helpful ability to have available.

ISO 639 changes frequently

The 639 language codes are actively maintained and altered by their respective registration authorities. This is not a hypothetical concern either, just see the change-log for ISO 639-3.

The use of the now deprecated language tag leaves me a little concerned about how actively the intl extension is being maintained; RFC 5656 was released in 2009, this is hardly a cutting edge standard.

Question

• Are the ISO-639 language codes used by intl updated regularly?
• Can intl be relied upon as an authoritative lookup resource for ISO 639?
  • If not, is there an authoritative lookup resource for ISO 639 in PHP?

The intl extension relies on ICU to supply language codes, among other things. The ICU version is stored in the constant PHP_ICU_VERSION. ICU itself relies on the Unicode Common Locale Data Repository (CLDR) as specified in the same documentation you cited in the Locale class: "The extensions used by CLDR in [Unicode Standard Annex] #35 (and inherited by ICU) are valid and used wherever they would be in ICU normally."