[Semi-OT]: How to customize locales?

Hi all, I’d like to use to_char function to return an already  
formatted result set. The it_IT locale (correctly) specifies a numeric  
group separator as “. ”, but I’d really want to use just “.”; not  
standard but much more common.
Anyway, the problem is that I didn’t find enough about how to create a  
custom locale. Does anyone have some suggestions/links?

PS Is there any way to use something like DateStyle with numbers? In  
this way, you could avoid using to_char.

Thank you in advance
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Giorgio Valoti