People’s names for themselves, and our names for them in English
It may seem odd, but a number of the names we use for peoples, nations and their languages are actually quite different from their names for themselves. Some, I expect, are better known than others.
Let’s take a look at just a few:
Greece, Greek. Own name: Elladha, ellinika
Finland, Finnish. Own name: Suomi, Suomen kieli
Hungary, Hungarian. Own name: Magyarország, magyar
Wales, Welsh. Own name: Cymru, Cymraeg
Germany, German. Own name: Deutschland, Deutsch
Armenia, Armenian. Own name: Hayastan, Hayeren
Georgia, Georgian. Own name: Sakartvelo, Kartuli
Basque Country, Basque. Own name: Euskadi, Euskara
Japan, Japanese. Own name: Nihon, Nihongo
So why do we have names for these nations that differ so greatly from what they call themselves? Well, there can be many reasons. Sometimes, names come from earlier tribes that lived in the regions now inhabited by others. A name might also come from a geographical feature. It may even come from a mistake, a name that’s misheard, or a mythological figure closely associated with that place. And once a name is there, it tends to stick, and it can be very hard to change it!
Glossologics 
There are probably more names for the Germans than anybody else, doubtless because they’ve been in the middle of Europe for thousands of years. (Indeed, they meet the official U.N. description of an indigenous people!) To themselves and the Italians they are ‘the People’; to the Finns they are ‘the Saxons’ (that is, ‘the knifemen’), which of course is what the Welsh call the English; to Western Romance speakers they are ‘all the men’ (probably from an old tribal alliance); to the Slavs they are ‘the mute’; in Latin and modern English they are ‘the spearmen’ (or possibly ‘the brothers’).