Most Chinese manufacturers only provide a short Chinese guide, but even renowned manufacturers such as Motorola or Apple do not have complete instructions nowadays.
It is generally assumed that the system itself is explored. In MIUI or emotion UI, it is very easy to find your way around, because both Android essays are quite self-explanatory. If you are more concerned, you can also find the little secret features. Stock Android smartphones usually have a small tutorial at the initial setup (software-based).