I have a particular interest in the languages of Mozambique. Many of these languages are heavily used in their local areas, but endangered by lack of acceptance in schools, lack of media in the language, and lack of resources (Possibly one of the reasons Moz is blank in the linked map).

I've found most of the best resources for actual text in smaller languages comes from religious translations, which can be a bit outdated but usually offer a fair amount of text. And beyond that I've gotten lucky with a few google drives and other repos mostly containing educational packets put together by various volunteer and missionary groups.

Unfortunately I'm not sure the copyright on many of those. I think that's why most of the language projects[1] I've seen wind up being mainly repos of titles of papers published on various languages. Which can be hit or miss for educational purposes.

[1] From the linked site I mainly poked at a couple African languages and didn't see much beyond the paper titles. There may be others with much more info.