This ranking by the Foreign Service Institute seems fairly plausible. I agree with the decision to move French up a tier, it is certainly harder than Spanish or Portuguese. My casual impression is that Romanian is a bit harder than the Iberian languages.
Not sure if the two tier gap between Swedish and German is justified.
Incidentally, I wonder how such a map would look for Slavic language speakers (does one exist?). Obviously the Slavic world would be all green, but I am wondering if the Latin or Anglo/Germanic languages will be harder for them.
Chinese is pretty easy, I am almost tempted to lower it a tier. Grammar is very easy; “long time no see” is a literal translation of a Chinese phrase that has made its way into English via immigrants. German or Russian grammar, to say nothing of Japanese, is far harder. It’s really only the characters that make Chinese a hard language, though obviously that’s a major component – even if it’s one of decreasing relevance.
Even so, it’s certainly no harder than Finnish – probably easier. I have a friend who is studying Finnish for idiosyncratic personal reasons. Although he’s mastered much of the torturous grammar and can use it in a “classroom” setting, he is still unable to understand Finnish people on the streets. Too much shortening of their overly long words.