AFAIK, there is no such thing in DB2 as to_char's nlsparam of Oracle.
And certainly for calendars, I believe DB2 only knows the Gregorian calendar.
Most likely there will be UDFs around to convert between calendars, but it seems that you will need to either manually apply this UDF after running ora.to_char, or modify ora.to_char such that it calls that UDF when necessary.