For those who might not know, Duolingo was started a few years ago by an American professor and some American university students (Thanks be to them). I had not realized that it was based on American English, but I guess that makes sense given Duo's origins. Until I did a little research into this subject, I thought most translations seemed to be British.
I am an American, and I said "Where are my eyeglasses" and lost a heart for it. Sigh.
As aucunLien reports, few in the U.S. says "spectacles." "Glasses" is probably used most; "eyeglasses" is more formal. "Spectacles" is apparently widely used in U.K., Middle East and many parts of Asia. Be aware that "la lunette" can also be goggles, telescope, or even "toilet seat". " Les lunettes" is used for glasses. http://www.larousse.com/en/dictionaries/french-english/lunette/47994
Yes, but pants in English are plural because it used to be two separate tubes of cloth that someone then had the ifea to sew together. Thus 'a pair of pants' (similarly for 'a pair of scissors').
I'm guessing the French had a similar situation with the development of pants. It's just a quirk of the language that french ended up with singular for pants and plural for glasses.