Hello i had this problem in january 2015, i have a full system installed in english, and properly reset to spanish by downoading the language packs, when i bought norton security with backup i updated with the installer provided to migrate from n360 to security with backup, and when i ran the installer it pop ups in spanish but after a few seconds it swaps to english, tested on another win 7 install with Fully Spanish settings and it overwrites it as well.
Suggestion improve the automatic installer