"The teacher is not American."
Translation:La maestra no es americana.
"La" is the only capitalized Spanish word in the translation selections. This, however, should not be the indicator as to how the English version should be translated into Spanish.
If it is masculine or feminine, then there should be a precursory indicator - like a pictorial depiction of the female teacher or verbiage indicating the teacher is female.
As this stands, it is too ambiguous and Duolingotites shouldn't have to infer masculine from feminine based on the translative selection post what needs to be translated...
It really depends on which format you get when this sentence comes up. If you are being asked to do the translation entirely by yourself, you should be able to translate it either way. If you are using a word bank (or get a "fill in the blank" exercise), however, then you need to make sure that your selections for "El/La," "maestro/maestra," and "americano/americana" all match in gender. For example, I would be correctly marked wrong if I entered a response of "El maestro es americana."
I kept getting this wrong because I was typing "el maestro no es americana" then it would tell me the correct translation of "la maestra no es americana. This confused me because I agree with everyone else that this should not demand specific gender translation exclusively due to the unspecified american sentence structure. Then I realized I was making the mistake of using the femine form of american which should have been obvious... I then retried "el maestro no es americano" and the translation was accepted. So as of 12/22/19 duo lingo does accept either gender if input correctly.