__Ogre__

Found the problem. WAY down at the bottom is a check box that says 'Change client messages to Polish' It is checked by default.

I recently downloaded the 9.15.1.06 mod installer and after installing it the in game language was changed to polish. Furthermore changing it in the World of tanks settings on the launcher does not change it back to English. I have downloaded a new world of tanks installer and completely reinstalled. That returns it to English but then reinstalling the mod pack changes it right back to polish.

Edited for additional notes:

I redownloaded the mod installer and made sure I selected the NA mirror.

I also uninstalled the mod and the language went back to English