Simple English Wikipedia
The Simple English Wikipedia is an edition of Wikipedia that's written in "simple English", essentially an in-house attempt to maintain readability by (1) using simple grammar and (2) limiting headwords to the 1000-3000 most common English words. The latter is somewhat dependent on field, with some fields naturally requiring more complex language than others.
The intended audience is children, English second language learners, etc. Many articles are simplified versions of the corresponding English Wikipedia article.
Its coverage generally is rather haphazard, and it is only a fraction of the size of the main English Wikipedia.
This may be a source of material for learners, but you've got to find an interesting article. English language learners may also contribute.
Attempts to shut the project down have, so far, been unsuccessful.