Right, so if this is done by trying to extend Daniel Verite's icu_ext extension (link given earlier) and Robert's idea of a fast-castable type, I suppose you might want now()::icu_date + '1 month'::internal to advance you by one Ethiopic month if you have done SET icu_ext.ICU_LC_TIME = 'am_ET@calendar=traditional'. Or if using my first idea of just sticking with the core types, perhaps you'd have to replace stuff via search path... I admit that sounds rather error prone and fragile (I was thinking mainly of different functions, not operators). Either way, I suppose there'd also be more explicit functions for various operations including ones that take an extra argument if you want to use an explicit locale instead of relying on the ICU_LC_TIME setting. I dunno.
As you know internally timestamptz data type does't existe instead it stored as integer kind and we depend on operating system and external library for our date data type support so i think that put as on the position for not be the first one to implement timestamptz data type thing and i don't know who give as the casting for free?
