There are over 2650 languages in the world plus over 7000 dialects. Deciding which language is the most difficult to learn may not be as simple as you may think. Different languages present different challenges, and what constitutes a difficult language depends a lot on the individual studying it.
Your mother tongue is an important deciding factor when it comes to difficulty. For example, native speakers of Italian seem to learn Spanish and Portuguese rather easily despite the complex grammatical structures of the Spanish language. On the same basis, Chinese speakers will probably pick up Japanese faster than people whose first language uses the Roman alphabet. In fact, Chinese has no grammatical system per se, which makes it easier to learn than many Western languages once you have memorized the basic characters.
Individual aptitude is another factor. Some people have a natural talent for learning new languages, while others struggle through the basics. Factors such as environment, materials used, motivation, and even environment also play an important role in how difficult a language is to learn.
All that aside, the British Foreign Office conducted a language study recently and concluded that the most difficult language to learn is Basque, spoken in parts of Spain and France, followed closely by Hungarian, which has 35 cases or noun forms. On the other hand, German and Russian languages use a punctuation system said to be among the most difficult ones in the world. Languages that use characters may seem hard to read and write to users of the Roman alphabet, but they are not always that difficult. Experts agree that Chinese and Korean can be learned rather easily by speakers of Western languages; Vietnamese and Japanese, however, are much more complex.
While many native speakers seem to forget this, English is actually quite difficult to learn because of pronunciation issues and irregular verbs; in English, many words are spelled the same but sound different depending on the meaning. This makes the English language hard to understand even for people whose native tongue is a related language.