which programming Language's are currently supported by DoxyGen ?

see the doxygen manual (e.g. https://www.doxygen.nl/manual/starting.html)

which programming Language's are planed that are supported by DoxyGen ?

none

is it planed, to support FPC (Pascal with object's, and with class'es) ?

no, but you could create a scanner and code scanner conforming the structure needed by doxygen like scanner.l / code.l, fortranscanner.l / fortrancode.l, pythonscanner.l / pythoncode.l or the way vhdl is supported or by means of a filter and be the maintainer of it.
There is already an external filter, but I don't know its quality / relefance, see: https://www.doxygen.nl/helpers.html