"Ich habe keine guten Freunde"
Very confused by this sentence translation. Duolingo says "I do not have any good friends" while it marks me wrong when I translate "I do not have good friends" or "I have no good friends". Is there an essential piece of this sentence I am missing? Why does "any" for the English translation become necessary? Also, why is "guten" singular for plural "Freunde"? To show the gender of the noun?
They key piece here is "keine," which, as you have seen, does not have a single English translation, but duolingo wants to make you translate it anyway. I think your translation, "I have no good friends," should be acceptable, as I was always taught that "no" is an acceptable translation of kein, so you might want to take that up with them. As for guten, guten is not singular here-- the -en ending is always used for plural words when the adjective is preceded by an article (der, die, das) or an ein- word (mein, dein, kein), as the preceding article or ein- word already indicates the gender or plurality.