According to the Foreign Service Institute (FSI), the following are the hardest languages for native English speakers to learn
Mandarin is difficult for English speakers, as it has a complex writing system with over 50,000 characters and four tones.
It has a complex grammar system with three grammatical genders and six cases. Its writing system is also very different from English.
Hungarian is a beautiful and creative language, there are 14 vowels with slight differences in pronunciation.
Japanese features three writing systems (hiragana, katakana, and kanji), and its grammar structure is quite different from English.
Korean has a unique writing system (Hangul) and sentence structure. It consists of just 24 symbols, of which 10 are vowels, and 14 are consonants.
Finnish is not an Indo-European language, making its structure and vocabulary distinct from many European languages.
Polish features a complex system of noun cases, gender agreement, and consonant clusters, making it challenging for learners.
Greek is the oldest living Indo-European language, including a lot of new vocabulary, three different genders for nouns, and complex grammar rules.