The Slavs didn't really think the Germans were deaf-mutes, surely?

Who knows, but it's similar to the ancient Greeks calling non-Greek speakers barbarian 'stutterers'.

[Addendum: Russian Немец (Nemets) 'German' is related to the adjective немой (nemoj) 'mute, speechless' (Leonard Nimoy's surname is probably related); other Slavic languages have related words meaning stranger, mute, stammerer, German, Northwind; the Slavic root is related to English mumble, German murmurln]


Ceci n'est pas un seing.