The hardest language to learn is Mandarin Chinese because of it's tonal nature, complex writing system with thousands of characters and the significant differences in grammar and pronunciation when compared to English.
The main reasons why Mandarin Chinese is hard to learn includes.
The tonal system as the meaning of a word in Mandarin Chinese can actually change drastically depending on the pitch of your voice, which is a concept that is not present in most Western languages.
The character based writing.
Mandarin Chinese unlike the Latin alphabet used in English uses thousands of complex characters which have to be memorized.
The large vocabulary gap.
Many concepts in Mandarin Chinese have no direct equivalent in English, and so it requires extensive vocabulary learning.
The number 1 language in the world is Mandarin Chinese.
Mandarin Chinese has over a billion native speakers and it's a significant language global communication.
Mandarin Chinese language is also know for it's tonal nature, rich cultural history and complex writing system.
The second largest native language in the world is Spanish which has over 527 million Spanish speakers.
English is the world's common language and is used in the United States by many people that are American and is used in technology, tourism and international business.
Portuguese is an official language in 9 countries, including Brazil, where around 98 percent of the population speaks the Portuguese language.
Russian is the official language of 4 countries although widely spoken in 19 countries.
Arabic is the 5th most widely spoken language in the world and has an estimated 313 million native speakers.
German is the 4th most used language and has 130 million native speakers and 230 million speakers worldwide.
The easiest languages to learn are most Germanic languages (Dutch, Norwegian, Danish, Swedish, and German) and Romance languages (Spanish, Portuguese, Italian, French, and Romanian).