How much effort are you willing to put into learning? Will you do homework, try to speak the language, read books on the language, listen to audios, and watch TV in the language?
– how different your first language is from the language you want to learn. For an English speaker, this is a list of languages in roughly increasing order of difficulty (in our opinion): Italian Spanish Portuguese French German Latin Greek Chinese Polish Russian Hungarian Turkish Japanese – your motivation, your effort, if you try to hear, read and speak the language outside of class.