I don’t know how many people in this community are interested in design and, of those that are, I imagine you know that Google’s Material Design documentation [1] is available in Japanese [2].
Personally I found the original design specification simpler, before they moved to material.io/, and for some reason the Japanese guidelines are provided as PDF documents which are even more difficult to browse and don’t include a table of contents.
That aside, I thought it would be good reading practise. You have the original English translation readily available if you get stuck or find the grammar confusing and it contains quiet a lot of loan words, which are relatively simple to follow and might make your reading experience less painful helping you pass that first page syndrome [3].