Field format : add language option

[fbaligand]

When we define a custom format for a field, it would be great to add an option "language" which allow to choose a custom language (like "fr"). It is particularly useful for number formats (thousands separator, decimal character, currency symbol).
Thus, it should be simple to implement, as numeraljs supports it natively.

[FraJern]

+1. this is something quite sanitary, to be able to get data on local formats or the option to set to local. just got the info that comma separated decimals is not supported in the numerical definitions.

[pchanas]

+1

[Bawazo]

+1

[sorenmh]

+1