You create a numerical question in french language using , as decsep and you use it in a frech language environment.
the grade is the same with 23,8 or 23.8 as response.
you answer the same question in english as language you get full grade in either case.
however the good response is shown with, or. following your language.
As long as we don't have specific grading for decsep used I agree with no penlty for decsep.
However the correct response display should follow.
This has been tested on actual moodle demo site.
Moodle 2.2.1 (Build: 20120109)
I am setting this a a bug so we can discuss what exactly we want for numerical question grading and decsep.