An End to Everything

51.7, 46.5 - worked for me turning in the Tongue.

Tongue of Ba-Shon can only be used in certain areas. If you complete a quest where you must use the item to communicate with Cho, you should stay in the area of the quest before moving on to do something else.

I had several other quests in the same general area. I moved on to do something else and then started looking around to try to turn in quests that required invoking the Tongue of Ba-Shon. I got a message about not being in the right zone. There are several quests in this chain that require you use the item, complete one and pick up next in the chain.

It seems that if you continue on to Zouchin Village before turning in this quest, Lorewalker Cho shows up in the village, and if you turn in the quest Fisherman's Tale, you will lose the tongue. When this happens, you currently have no way to turn this quest in.

The moral of the story is: Don't forget to turn this quest in while you're in the Valley of the Emperor because if you wait until afterwards, you may not be able to complete it.