I would start from a FM like DAY_ATTRIBUTES_GET, MONTH_NAMES_GET or CONVERSION_EXIT_LDATE_OUTPUT [CONVERSION_EXIT_JPDAT_OUTPUT for japan ?] and look for notes at SAP, or even raise an OSS message. You could also look at Best Practices solutions for countries like Poland or Hungary.
You could also look at ddic and find some tables like
| T015M | Names of the months |
| T247 | Month name and short text |
| TFARSIMONTH | Names of months of Farsi calendar |
| TISLMONTH | name of months in Islamic calendar |
Regards,
Raymond