After installation in Spanish, half of the applications is still in English

 I have installed Mint Main Edition DVD 32 bits. After clicking "Install Linux Mint", I selected Spanish the installation went trough in Spanish, I rebooted and then half of the system is in Spanish and other half in English.

 Applications shown in Spanish:

 - Mint Update
 - Mint Menu
 - Mint Nanny
 - Welcome window

 Applications shown in English:

 - Nautilus
 - Firefox
 - LibreOffice
 - Thunderbird

 Interesting enough "Control Center" is shown half in Spanish, half in English.

 I was supporting someone who doesn't speak English, and it was difficult for him to follow.

 The work-around is to go to the "Control Center" and choose "Language support". Then it says that the "Language support is not completely installed" (this message in Spanish). I click on "Install", then I authenticate (message in English), then the "Language support" window greys out for two minutes without any feedback. When the window recovers, I try to select Spanish, but it is greyed out. So it seems that installation didn't go trough. In the same window I click in "Install and delete languages" and I see that Spanish is installed!!
 I then close all the windows, logout and login again and everything seems to be in Spanish!!
 So at the end everything is as expected, but the user experience is really really painful, and discouraging for newbies who don't speak English.
 It looks to me that this is something important to take care, because it is the first contact of a first user with the system, and usability is important at those first stages.

 Best regards,
 Enrique