It's also labelled as in beta. After signup, it clarifies what that means at the bottom of the page: > Note: Readlang has only limited support for 日本語. Words a

It's also labelled as in beta. After signup, it clarifies what that means at the bottom of the page: > Note: Readlang has only limited support for 日本語. Words are not prioritised based on frequency, and texts are not graded by difficulty. Slightly disappointing, as I really hoped they did that, but I'll probably still give it a try. EDIT: I'm very impressed by the translation.