Windows 7 - Installare il MUI su windows 7 professional

MUI you can install also in Professional version from MSDNAA,
just follow this steps:
from admin account type in CMD: 

DISM /Online /Add-Package /PackagePath:[b][i]patch_of_lp.cab[/i][/b]

next:

bcdedit /set {current} locale [b][i]es-ES[/i][/b]

and:

bcdboot %WinDir% /l [b][i]es-ES[/i][/b]

next, using regedit delete en-US from:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlMUIUILanguages

Reebot Your system and enjoy