How much do these glasses cost?
For anyone coming across this sentence and wondering about Brille vs Brillen, the following comment is posted on the Tatoeba page for this German sentence -
*Wie viel
Brille (Singular) heißt im Englischen “glasses” (Plural), in Esperanto “okulvitroj” (Plural). Normalerweise würde man den englischen und den Esperanto-Satz also mit “Wie viel kostet diese Brille?” übersetzen.
Die Übersetzung im Plural ist aber nicht falsch.
Interesting words.
For a German native the use of the plural in other languages is just as puzzling.
Of course, “eine Brille” consists nowadays of two “Brillengläser” (glasses).
And whereas the Englsih and the German word refer to the material (in German from “beryll”, a mineral the first visual aids in the 13th century where made of) the Italian word refers to the eye. Esperanto seems to be a synthesis of both.
From beryll! Great to know. Vielen Dank!
The French went for the small moon shape of the lenses, adjusting the plural to the number thereof:
Don’t forget English also has the word “spectacles”, from old Latin “specere” (to look), related to “spectaculum” (public show). But why the word is pluralized in English is anyone’s guess! 
