I have made a few contributions to the regular English Wikipedia and now am helping a bit on Simple Wikipedia. I have some technical background in science and mathematics.
I am struck by how difficult it is to write "simple" articles in simple language about many things. It is very challenging to avoid or at least minimize circular reasoning.
I try to restrict the articles to only use the words in the Basic English 850 list, but this results in very stilted language and constructions many times.
I try to make the articles very simple in content as well. This is not at all easy, especially if the topic of the article is somewhat complicated.