I can’t set it up. Everything is in Chinese.

If the setup was already completed:

1. Go to the home screen, by pressing Menu or < Back until you get there.
2. Find the gray Settings icon with the sprockets wheel . Open it.
3. The top option is General. Open that.
4. The 8th option on the next screen is Apple TV languages. The image on the left should now change to a globe/​earth-like symbol.
5. The last option (with ⋯) on the next page is for adding new languages. Select that.
6. The next page has the list with languages, each language named in their own language (with system language translation below that). Select your language of choice.
7. On the next page, confirm by selecting the top option (① Use this newly selected language). [The other options are for ② Keeping the previous setting (but add new one as secondary), and ③ Cancel. Then Apple TV will now update the used system language to reflect the change.
8. For ‘English’, you may want to change it once more, to select the wanted dialect, e.g. ‘English (US)’, which will have an adjusted word list (e.g. TV programmes vs. TV shows).
9. There is an Edit option at the top if you want to remove the initial language from the system.