There is no "Arabic Dating" or "Thai Dating", they are religious calendars.
In most cases there is no simple 1:1 correspondence to the Gregorian dates, since
(a) some of the calendars are lunar or lunisolar (means the year length is different from the solar year, even variable)
(b) there is an offset between the calendars (means their year does not start on 1st January, not even on the same AD date every year)
(c) the various practices of leap years is complicated, to say the least.
To make it short, take any year in an Islamic, Buddhist, Jewish calendar and you always have two possible Gregorian years. Only by knowing
the exact day you can decide which one it is.
BTW, there is a nice freeware tool "Calender Magic" which does a lot of calendar conversions.
... and for my taste, to call all these dating systems "unusual" is a bit too Euro-centric
cheers
--
Harald