It certainly is subjective, but it seems that Duolingo focuses on reading the language, so from that perspective, Japanese (and related languages such as Chines

It certainly is subjective, but it seems that Duolingo focuses on reading the language, so from that perspective, Japanese (and related languages such as Chinese and Korean) will be more difficult. Unfortunately, I find learning the written portion of languages to be the easy part - learning to speak and hear the language is much harder.