As well as the various more serious issues already mentioned by people (such as open chiitoi) the most confusing part I found was at the end of a game. It's not obvious what to click, the first few times I just closed the client.

An article about Jenn located here, says

Additionally, she’s finishing up a book on mahjong in English, the first publication of its kind.

So it will be in English.

Edit: I should also add that the article was written by a user of these boards, and is a fairly interesting read.