i think that jalali date is a thing that the developer could add in 0.09.6 release. it make the MODx more compatible with other languages.
I do not see how this is something the MODx core needs to deal with, but rather a PHP responsibility.
PHP’s Calendar extension is optional and does not support the Jalali calendar that I know of. However, there seem to be a number of PHP solutions for utilizing Jalali dates. I would suggest looking into using one of the many available solutions that might work within your MODx add-ons.