My client had a problem with an update of Adobe Reader version 11.
After updating, only english was available.
The update was a MUI version …

After verifying the files and folders, I noticed that the “Locale” folder wasn’t created.
I installed Adobe Reader 11 MUI normaly (not in silent mode) and choose another language then English.
After the installation just copy the “Locale” folder in the Program folder of Adobe Reader.
C:\Program Files (x86)\Adobe\Reader 11.0\Reader\Locale

I copied the “Locale” folder into the Customization Wizard and overwrote all files.