The number of natural languages

[xfq]

https://tc39.es/ecma402/#sec-implementation-dependencies

Linguists estimate the number of human languages to around 6000

Regarding the number of natural languages, most people refer to SIL International's Ethnologue, and there should be more than 7,000 languages ​​now.

[aphillips]

An exact number is not realistic. Linguists (and others) disagree about the exact definition of a language and famously there is a tension between "splitters" and "lumpers". So it would probably be better to say something more like:

Linguists recognize over 7000 human languages

But I'd probably rewrite the whole paragraph.

Original:

The set of locales that an implementation supports with adequate localizations: Linguists estimate the number of human languages to around 6000, and the more widely spoken ones have variations based on regions or other parameters. Even large locale data collections, such as the Common Locale Data Repository, cover only a subset of this large set. Implementations targeting resource-constrained devices may have to further reduce the subset.

Suggested:

The set of locales that an implementation supports with adequate localizations: Linguists have described thousands of human languages, with the IANA Language Subtag Registry containing over 7000 primary language subtags (used as the base for locale identifiers). Even large locale data collections, such as the Common Locale Data Repository, cover only a tiny subset of all languages and their regional or dialectical variations. Implementations targeting resource-constrained devices may have to further reduce the subset.

[xfq]

Indeed, I think your proposed text is better.