Open the avast interface.
Click on the text on the left side of the wrench.
Now, the settings pop up.
On settings, go to 11th line on the right side.
The language settings appears.
Click the gray button on the left side, and another pop up appears.
Select English and press enter on your keyboard.
Press enter to close the settings window.
The language will now turn into english.
Go to the avast website.
Download the English version of avast http://www.avast.com/free-antivirus-download
and avast uninstall utility http://www.avast.com/uninstall-utility
Reboot computer into safe mode by pressing f8.
Run the avast uninstall utility.
Start avast installer and select only English.
Once the installer is done, it displays the program in English.