Its happening because the language add window is a small popup and when you let your token expire it cant display the message on the smaller window so it gives you a parse error.  

Then when you close that window, the token expire displays. 

To repeat this do this: 

1. Add a couple of new key values in language under a plugin name

2. let it sit (with smaller window closed) and let the token expire (21min)

3. add another language key same plugin 

4. you should get a parse error

5. close the smaller window

6. the token expired notice appears. 

Thanks :)

I am interested in how they fix this because in some of my plugins i may have a popup as well in the future and it would be good to know how they fixed this.