The separate input element for the numerical value give us the opportunity to define the number formats that will be valid in numerical and calculated question types.
The is_numeric() PHP function accept numerical with various exponents expression (and also Hexadecimal notation (0xFF) is allowed too but only without sign, decimal and exponential part. )
This is derived from the C language format() function.
The apply_unit() extended the use of . to , and eliminate spaces so 3 000,34 is a valid number.
This could be extended further to take account of the specific country at the Moodle installation level.

The actual proposal include a string (qtype_numerical) that could be modified locally if necessary (if the code is modified locally)
The main objective is to give to the student the informations on how to fill the response number field with a valid value.
Additional informations about units or penalty schema can be added by the teacher in the instructions field.

We could also explore ways to add other numerical representations like fractions 1/3 that could be applied to numerical without adding to much complexity to the editing interface.