Dake?

So in my school Japanese textbook, it says that the word "dake" (only) replaces the particles ga, wo, ni, and de. I thought this was weird because i've heard from my friends in Japan use "dake" and "ga" all the time. it gave this example in the book:
tomodachi to chuugoku dake ikitai desu. 友達と中国だけ行きたいです。 - I only want to go to China with my friend.

My friend said that it should be tomodachi to chuugoku ni dake ikitai desu. 友達と中国にだけ行きたいですor tomodachi to chuugoku dake ni ikitai desu. 友達と中国だけに行きたいです。

The book has made me very confused! If someone could explain, that would be great :)

友達と中国だけ行きたいです。is fine without に.

Normally 中国に行く is correct but when using だけ, you can omitに - 中国だけ（に）行く.

But the translation should be ''I want to go only to China with my friend.'' (Only to China, no other places)

If ''I only want to go to China with my friend.'', it is 友だちと中国に行きたいだけです。

友だちとだけ中国に行きたいです。
I want to go to China only with my friend.

Not all text books are correct all the time.
友達と中国だけ行きたいです。 I want to go only to China with my friend.
You can add ga, ni, wo, de, ha to emphasize.
友達と中国にだけ行きたいですor 友達と中国だけに行きたいです。I want to go only (limited) to China with my friend.
I want to go to China only with your friend, 友達(と)だけで中国に行きたいです。
At least I want to go to China with my friend.友達と中国だけは行きたいです。
I want to drink only beer,ビールだけを飲みたい。　
Only I can do it. 私だけが出来る。