Hello, what i did was get the *en.us.lang* file from the 'assets' folder in the '1.11' folder. In my computer, the folders are like this:
.minecraft --> versions --> 1.11 --> assets --> minecraft --> lang
I copied and pasted the english lang file (*en.us.lang*) into my pack and then i modified what i wanted to change, while leaving everything else there and it worked. it might work for you too as long as you keep the rest of the file text there, even if you arent gonna change it.