Adding pinyin for chinese system wide

I learn Chinese and live in China, me and my friends find it difficult to read Chinese, so pinyin (Latin transliteration) is really helpful to speed up learning and productivity in fully/Chinese apps.

Some of my friends shared how they change the system font, so it can display the correct pronunciation of each word in Chinese on top of it. So far I could not find a way to do it in iOS. I wish Apple could provide an option for that.