You will need three files:
1. Sysprep.inf
2. sp_unattend.bat
3. sp_unnattend.txt
In the [GuiRunOnce] section of the sysprep.inf add:
Command# = "C:\Windows\COE\sp_unattend.bat"
The sp_unattend.bat should contain:
rundll32 shell32,Control_RunDLL intl.cpl,,/f:"path_to_file\frunatnd.txt"
The sp_unattend.txt should contain (french example):
[RegionalSettings]
MUILanguage = 040c
MUILanguage_DefaultUser = 040c
