The Translation Service has prepared a bilingual list of the names of states, territories and stateless nations.
A full version of the list can be found on this page. The list includes English-language names, standardised Welsh-language names, and some notes.
All these names can be found in the TermCymru database, where you can search for them individually. This resource is published under the OGL licence, as are all the Translation Service's resources on BydTermCymru.
Standardisation of the Welsh-language forms are based on a set of principles formulated especially for this work. The principles are published in full (in Welsh) in the Arddulliadur, under the title Dynodi enwau gwladwriaethau, tiriogaethau a chenhedloedd diwladwriaeth.
Please note that this list is intended to prescribe specific forms for the Welsh Government Translation Service's use. Other forms may be equally valid, in other contexts.
Also note that the standardised forms may change with time, in line with the principles, and the list may be expanded in due course.