Is there a full list of codes in ISO-639-6:2009 (Codes for the representation of names of languages — Part 6: Alpha-4 code for comprehensive coverage of language variants) such as a cached mirror or repository? The original registry GeoLang no longer provides the query services as shown in this archived page. I know that it's currently deprecated but it's good to know the completeness of the system.
Most likely, there never was a complete list. In October 2014 Peter Constable wrote the following in an e-mail to the IETF-languages mailing list (emphasis mine):
While ISO 639-6 did get approved and published, the code table for 639-6 has never been made fully available in a usable manner. What data has been available has been looked at by lots of people with a response that they don't find it particularly useful for any practical application. Moreover, the agency that was designated as registration authority appears to have ceased its operations. In a nutshell, 639-6 had in many respects failed.
The agency referred to in this message is GeoLang (as mentioned in the question). Technical committee ISO/TC 37/SC 2 lists ISO 639-6:2009 as a "withdrawn standard".
Based on the clues from language wikis, it's very likely that there was a full list. What I don't understand is that it's a great project first time in human history to codify almost every language and dialect in the world. Standardization is important for usage in data science and computer programs. Yet it's deprecated with such absurd excuses. There is not even a backup. So many years of effort are completely discarded... I can't find anything more confusing and annoying than this... Dec 25, 2021 at 18:27
@EurekaZheng In standardisation, terminology matters. The standard was not "deprecated"; it was "withdrawn". Note also that the standard itself did not provide a list but only criteria for such a list.– TsundokuDec 25, 2021 at 18:55
@EurekaZheng Important for data science and computer programs? Most of the time, ISO 639-1 is enough; Wikipedia has only 5 Wikipedias in the 50 largest that need an ISO 639-3 code. And we have 639-3. Few need more details of ancient languages or dialects of modern ones, and those that do know what they need more than any one-size-fits-all standard could. Not to mention that ISO 639-3 has enough questionable, problematic areas just listing languages; trying to standardize dialects and poorly documented ancient languages would likely standardize a bunch of errors and be useless. Apr 29, 2022 at 21:11
A full list of world dialects with authority control serves as a useful index for digital linguistics research, besides Wikipedia. Jun 25, 2022 at 21:43