So איזה and איזו are the singular masculine/feminine forms for "which." Does that mean that the plural forms are אילה and אילו? Are they used much in colloquial Hebrew?
Good questions! I was working out some of these semi-familiar forms as well. The notes have the singular forms as איזה (MS) and איזו (FS), and the plural form as אילו.
Duoling's Hebrew "Tips and notes" state:
"You will find that in Modern Hebrew people very often just use the singular masculine form, איזה, instead of the plural אילו, and to a lesser extent, איזה instead of the feminine איזו for feminine nouns. You should try to refrain from this habit, although we do often allow these technically incorrect answers due to the frequency of occurrence among native speakers."
Edit: I corrected the above forms since I had misread the notes.
You say "You should try to refrain from this habit" - why? In Modern Hebrew, איזה is the default form for the question "which", so if you, as a native or fluent speaker, know your thought begins with which you say איזה before you even think about grammatical gender and number of whatever follows. Of course, practicing grammatical agreement will help new learners learn how agreement works in Hebrew, but refraining from speaking in a manner used by most native speakers sounds like less than useful prescriptivism.
Hi, Jay. Actually, I didn't say that. That's part of a quotation from the "Tips and notes" for Duolingo's Hebrew course. Your question is a fair one for the course contributors. I would agree with you that grammaticality can't be severed from actual usage.
I would translate this sentence as "Which animals do you like?" or "What kind of animals do you like?"
In any case, it does not strike me as the way you would phrase the question either in Hebrew or in English. In Hebrew, I think I would use "איזה מין חיות אתם אוהבים?"