Do you think they're difficult?
I'm Vietnamese. I don't a lingguist, but think there are more different between every language and each of them has some particular special. However, Vietnamese is not difficult to learn, if you want we could exchange language. in almost of people in Vietnam, they said that Japanese is most hard to learn <img title="Cool" src="http://www.italki.com/Scripts/tinymce/jscripts/tiny_mce/plugins/emotions/img/smiley-cool.gif" alt="Cool" border="0" />
I'm not sure what Vietnamese is like, but I know that Chinese is very hard, and Thai looks very complicated.