I think I managed to solve the problem: it was caused by the special situation of the Italian locale, which has the decimal separator set as the same as the thousands one.
Actually, in the italian language is a rule since a while that no separator should be used for the thousands, but only a space (at least, this I clearly remember from the elementary school), but often in software the "." is used. The separator for the decimal is the comma, and this is correct in OpenAcs.
In other software I had to work on, the company had created a customized set of procedures to handle number formatting, so we never incurred in the problem.
Anyway, I looked into the lc_parse_number code: it first removes the thousands separator, and then converts the decimal separator to a dot. This leads to the problem, as in the italian locale it erases the comma used for the decimal before it can be detected.
I solved putting a few lines of code in which it firstly detects the last decimal separator (whatever it could be) an splits the number into its integer and decimal parts, then it removes the thousands separator from the integer part, and finally joins the two parts again using the dot.
This fixes the special situation of locales using the same separator for both decimal and thousands.
I then tried to put the "right" thousands separator in the translations. I could insert a space as "\ " and checked the proc output for "12 000,00": it is parsed correctly as "12000.00".
I can provide the modified localization-procs.tcl, which comes from oacs-HEAD installed just the other day. I also suggest to switch the thousands separator from "," to "\ " or "." for the Italian locale in standard installation, as the comma is really unusual.
All the best
Antonio