speaking as someone with experience in dutch + written mandarin, neither I found are partically difficult.
Though I couldnt say which language is, perhaps finnish is.
had a quick google
http://www.nvtc.gov/lotw/months/november/learningExpectations.html
whilst im no expert but it does seem reasonable, eg german is slightly more difficult than dutch
heres another one
http://languagestudy.suite101.com/blog.cfm/language_difficulty
of course these are from an english speakers perspective,
Though I couldnt say which language is, perhaps finnish is.
had a quick google
http://www.nvtc.gov/lotw/months/november/learningExpectations.html
whilst im no expert but it does seem reasonable, eg german is slightly more difficult than dutch
heres another one
http://languagestudy.suite101.com/blog.cfm/language_difficulty
of course these are from an english speakers perspective,