Deutschland, Germany, Allemagne, Niemcy, Saksa: one country, five names.
An endonym is the name a group gives itself: Deutschland. An exonym is the name from outside: Germany in English, Allemagne in French, Niemcy in Polish, Saksa in Finnish. London likewise becomes Londres, Londra, Londyn. The UN Group of Experts on Geographical Names wants fewer exonyms, but admits many are cultural heritage and fast replacement is unrealistic.
Useful: Looking up a place in a foreign language, you need its exonym there; map apps help, station boards don't always.
Source: en.wikipedia.org