GLIBC and CLDR register similar things. They register for similar but different purposes. One is a standard and the other is a de facto standard.
When people with the right background take an interest in a language like Sourashtra, they can have many objectives. What we are looking for are people who are interested in enabling, supporting and promoting the use of their language.
When a font is needed and they can point us to a freely licensed font, we can support them. When a keyboard is needed specifically for a language or a script, we can support them. When they provide us with the code to transliterate from one script to another, we can support them.
To do this for one application is a lot of work and there are so many applications out there, so much replication is happening. Many of these applications are as useful and relevant as MediaWiki. It is for this reason that all the language support teams are asked to verify and possibly amend and append standards like the CLDR or GLIBC.
With information available in the right places and with fonts, keyboard mappings and transliteration scripts shared widely, in a perfect world there will no need to ask to verify, amend and append. By working together using the same data, there will come a time when there is no longer anything to amend or append, when the data for a language new to Wikipedia will just be there.