There are several language code systems and several region code systems, as well as their combinations. As you refer to a W3C page, I presume that you are referring to the system defined in BCP 47. That system is orthogonal in the sense that codes like en-GB and fr-CA simply combine a language code and a region code. This means a very large number of possible combinations, most of which make little sense, like ab-AX, which means Abkhaz as spoken in Åland (I don’t think anyone, still less any community, speaks Abkhaz there, though it is theoretically possible of course).
So any list of language-region combinations would be just a pragmatic list of combinations that are important in some sense, or supported by some software in some special sense.
The specifications that you have found define the general principles and also the authoritative sources on different “subtags” (like primary language code and region code). For the most important parts, the official registration authority maintains the three- and two-letter ISO 639 codes for languages, and the ISO site contains the two-letter ISO 3166 codes for regions. The lists are quite readable, and I see no reason to consider using other than these primary resources, especially regarding possible changes.