I just don't know how I was supposed to know "sandwiches" was a valid plural form as well.

I am a native German and "Sandwiche" seems very unnatural to me. It might be gramatically correct, yet I don't think anybody would say that but rather use the usual English pural, "sandwiches". Also I think that one could simply translate "a sandwich" as "ein Butterbrot" which most people say whenever they make themselves a sandwich. Some people say "eine Stulle" as well.

Okay, so if both "Sandwiche" and "Sandwiches" are correct, then why is it that earlier, when I spelled it "Sandwiches" it flagged me as being wrong, and to spell it as "Sandwiche"? Duolingo really needs to make up its mind.

are these both plural then? or is it rather that the singular for certain foods (like meat?, e.g. i eat meat and i eat meats - odd but possible) can be said in both the singular and plural forms?

I think "Sandwich" is singular and "Sandwiche" is plural.

no idea... wanna know too