Proper and Improper Names

The Czech word for 'German' - němec comes from

němci - "mumbling, murmuring people"
(from Slavic *němъ – "mumbling, mute, incomprehensible, or stupid").
The same word (német) passed into Hungarian.

The alternative English word for  'ass' - donkey
- comes from Duncan, a popular Scottish forename
which means dark-skinned important person or warrior
of the Mesolithic (dark-skinned, not-tall) genetic type
 which is to this day to be found in Ireland.
The Scotti were people from Ireland who colonised Alba
(Scotland); the ancient alb-element, meaning snow, white,
or a high place which attracted snow, gives us Alp,
Albany, Albion, Albania. 

Ireland (Latin Hibernia - Winterland) is named after
an obscure early earth-goddess Éire.

The Rus element of 'Russia' (Rossiya) comes from Ruotsi,
the Finnish word for Sweden, because of the Swedish Vikings
who lightly colonised the gold/amber corridor through Western Russia
and Ukraine to Constantinople or Byzantium
(which they called Miklagard = Great City).
The Finnish word for 'Russia', however, is Venäjä - I don't know why -
and for 'Germany' is (unsurprisingly when you think of the geography) Saksa.

The English word Slav, like the French word slave
seems to have been borrowed from Medieval Latin sclavus or slavus,
itself a borrowing - and from Byzantine Greek σκλάβος (sklábos) 'slave'
into which the Emperors of the East turned some Bulgarians
(who, amazingly, gave the words bugger and buggery to English
and Bougre to French. Modern Bulgaria was a place of many Bogomils
or Cathar-Albigensians.)  The Nazis must have liked this consonance.
Not all Nazis were German-speakers. There are no more
'Hellenic' Greeks than there are ancient Roman Romanians.

The Slavic word for Slav comes from slovo = 'word'
- indicating those who spoke an understandable (Slavonic) language
and not Hungarian, Finnish, Romanian, Vlach, Albanian, Greek
or babbling barbarian German.