A national standard of exonyms is needed in every language. Look at some examples of exonyms taken from Dutch atlases, before exonyms were standardized there:

Bosatlas ('76)	Oosthoekatlas ('78)	Meulenhoff atlas ('78)
Haleb (Aleppo)	Aleppo	Halab (Aleppo)
Bur Said (Port Said)	Port Said
El Suweis (Suez)	Suez	As Soewees (Suez)
Dimachq (Damascus)	Damascus	Dimasjq (Damascus)
Mina Hassan Tani  (Kenitra)	Mina Hassan Tani  (Kenitra)	Mina Hassan Tani  (Kenitra)
Tarabulus (Tripoli)	Tripoli	Tarabloes (Tripoli)
Khartum	Khartoum/Khartoem	Al Chartoem
El Djezair (Algiers)	Alger/Algiers	Al Djazaair (Algiers)

Blue line = source