Internationalization best practices

Hi,

How do you usually do when you need to create an application with users in differente country with different timezone and date format?
I know that cakephp date and datetime use the locale settings for formatting, but sometimes this is not enough.
I need that a user in the frontend could set datetime in his timezone and time format, but internally the whole application could use UTC timezone and en_US time format.
The DB use this format too.
Where and when you convert the date arrived from a form, with the user timezone and format, in the system timezone and format?

What are the best practices for handle localized user input?

I don’t like standard cakephp system, that localize the date db type because it changes the whole application, and not only the user input features.
Automatic datetime localization, change how a date is displyed not only in a template but in place that you don’t want too.
For example, if internally i use the yyyy-mm-dd date format, but my user locale is it_IT, the date format will be dd-mm-yyyy.
when i create a form with that date field, the field will automatic filled with the entity value, but because of the localization settings, the field will be filled with the date in it_IT format, and not the system format. So i need to create an automatc conversion system.