The difficulty of learning a new language depends on the intensity of instruction, previous language experience, and above all motivation. The National Virtual Translation has outlined various levels of proficiency and the length of time required to achieve a ‘level 3’ of proficiency for English speakers.
For example, to become proficient in Swedish takes approximately 600 hours, whereas Arabic 2,200. People often wonder what is the ‘most difficult’ language, anthropologists agree that there isn’t one. It’s how different a language is from your mother-tongue that determines that.