When did Constantinople change its name to Istanbul?
Names of Istanbul
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Names other than استانبول (İstanbul) had become obsolete in the Turkish language during the late Ottoman/early republican periods. However, Constantinople was still used when writing the city's name in Latin script. In 1928, the Turkish alphabet was changed from Arabic script to Latin script. After that, Turkey started to urge other countries to use Turkish names for Turkish cities, instead of other transliterations to Latin script that had been used in the Ottoman times.[20] Letters or packages sent to "Constantinople" instead of "Istanbul" were no longer delivered by Turkey's PTT, which contributed to the eventual worldwide adoption of the new name.