"Sorry, there are no dictionaries available for this language. Language: English (United States)"

I've had the same problem and no where online is there an answer.

So I messed around and here's what worked for me.

I went to the Insert tab on the ribbon --> and clicked on Store (orange icon in Apps), it opened a store window and i searched for dictionary - downloaded merriam webster just for fun - download whatever you want.

I then went to the store via the windows interface and went to my Account and chose to switch user - then signed in with my info again. the first time it didn't do anything but give me the busy circle of dots spinning around, so I cancelled and tried again, it worked. Then I went back to word - to my account and did the same thing, switch account signed in. 

Typed a word, right-click - define - boom it pulled up the dictionary I installed (which didn't work before before it seems to be a sync connection error between the store and word. 

Let me know if this worked at all for you.

I don't yet know if it's a permanent solution, only time will tell.