I'd like to combine english UI language with belgian culture data (text direction, decimal separator, date format etc). This should apply to my Odoo users (collegues).

Because the languages are shared for internal and external purposes, I intend to duplicate the en_US language record and change the culture data. This is _not_ possible because of the requirement "The code of the language must be unique". Creating a new language record and setting everything up manually is also not possible.

So here are my questions;

* WHY is that requirement there?

* How do I properly setup a language record with language code en_US, different from the pre-existing en_US, with modified culture information?

Fudging with the language codes works partially, some modules (Accounting) throw a language related UI error on opening.