Technically, 'this species IS rare' doesn't make sense in English because species is plural, right? Shouldn't it be specie?
species can be both singular and plural
No. Species is the singular, the plural is also species.
I came to learn French, now I'm learning English
this is a very rare species . Not accepted. Why
As you are learning the language, try to translate it closely to the original form. This species is very rare. The meaning is the same but there is no need to switch it around.
You can back-translate what you wrote to a different French sentence, so it's not an accurate translation - C'est une espèce très rare / Cette espèce est très rare.
Shouldn't it be cet and not cette, aren't they breaking the double vowel rule.
No. "Cette" is feminine, "cet" is masculine and is put before vowels to create a liaison and "ce" is also masculine, but put before consonants.
because the final "e" in "cette" is not sounded "cette" can be used before a word starting with a vowel
Isn't the word 'very' redundant when referring to 'rare'?
well, no...not really. Things can still be gradated as rare-rarer-more rare-very rare-the rarest. E.g. Gold is rare on earth, but helium is very rare.
I answered "This species is rather rare" and it wasn't accepted. It should have, right?
For learning purposes, consider "très" = very.
espèce can also mean type. This type is very rare should be accepted - it's a different context but the context isn't specified!!