Deciding the hardest language to learn depends on your native language. For example, English is a language that blends elements and words from Germanic, Romance, and Anglo-Saxon languages. Because English is so heavily influenced by these three language families, other languages in those families are closely related to English and a little easier to learn than languages that are in entirely different categories. German and Scandinavian languages tend to be the easiest, closely followed by French, Spanish, and Italian. Even Middle Eastern languages have some elements in common with English.
The hard languages for English speakers tend to be Asian, African, and Native American languages. But there has to be one language that's harder than all the rest, so let's take a close look at a few of the world's most complicated languages to better understand which one might be the hardest of them all.
In Asia, there are a lot of languages that are extremely difficult because of their writing systems. Chinese uses the Hanzi writing system, with 50,000 characters, with each representing a word or syllable. However, to be a fluent reader and writer of Chinese, many studies estimate that you only need to know around 3,500 characters. There are benefits to the system, as well. For instance, China has many dialects of Chinese that are very different from each other in the spoken language, but all Chinese dialects share the same writing system. So, if you learn to read Mandarin Chinese, you can read all of the dialects of Chinese. Another thing that balances out the difficult writing system in Chinese is its easy grammar- there are no tenses, plural nouns, or gendered articles in Chinese, so in the grammatical sense it is far less complicated than languages based on Latin.
Japanese has borrowed thousands of Chinese characters for use in combination with their much simpler hiragana and katakana alphabets, where each character represents a single phonetic sound in a manner similar to Western languages. Korean also has a simple alphabetic writing system where letters are combined into blocks representing syllables. But Japanese and Korean have extremely complex grammars with many tenses and word orders that are not familiar to speakers of English. Finally, there is Vietnamese, which has been written with a system of Roman characters, just like English, since it was colonized by the French in the mid-1800s. But even with the Roman characters, the complex accent marks and diacritics that are added to almost every letter make correctly pronouncing every word with the right vowel sound and voice pitch very difficult.
In Asia, the two hardest languages that are also highly relevant and useful for international relations are Chinese and Japanese. Chinese is difficult because the speaker must master forming and hearing the proper voice pitches, or tones, associated with each word, and because its writing system requires the mastery of 3,500 complex characters. Japanese is difficult because it uses a writing system similar to the Chinese system, with an additional two alphabets that must be interchanged throughout the writing, and because it is full of unique and perplexing grammatical structures that have to be processed and assimilated into the speaker's subconscious. Additionally, the non-verbal part of spoken communication can be critical to learning the language- there are many gestures, omissions, and common courtesies that are hard to understand for Westerners that must be learned as part of communication in Japanese.
Africa is one of the least developed continents on the country, and it is full of ethnic groups and isolated cultures that strongly hold on to native languages and customs. Thousands of languages are spoken on this continent, including some of the most difficult in the world. Swahili, Hausa, and Zulu are three languages that are used as a lingua franca in different regions of Africa, meaning that speakers of various languages use the one of these three languages for communication between ethnic groups or tribes.
The languages of Africa are difficult for English speakers largely because of the sounds that are often used throughout the continent. In Africa, languages make use of multiple clicks, double-stop consonants, and implosive consonants. If these linguistic terms sound strange to you, it's because we simply don't have those types of sounds in English. Grammars can be complex as well- Unlike Chinese, which doesn't even pluralize nouns, Swahili has sixteen noun cases- six for singular nouns, five for plural nouns, one exclusively for abstract nouns, and several more. It is difficult for speakers of a non-African language to understand the meanings implied by each noun case. Then again, maybe Swahili isn't so hard after all- Millions of children around the world have learned how to say "Hakuna Matata" from The Lion King.
Finally, we move to the Americas. The Native American tribes of North and South America had been living in complete isolation from Europe, Asia, and Africa for thousands of years before Vikings and Spanish explorers sailed across the Atlantic Ocean. Because of this, their languages developed in an entirely unique direction often with characteristics that are very abstract for English speakers. Today, many of these ancient tongues are on the verge of extinction, with only handfuls of speakers still living. But there are still some strong languages and many new programs aimed at teaching young people how to speak Native languages, like those at the University of Oklahoma.
A unique feature found in many Native American languages is agglutination. Everywhere from the Eskimo-Aleut regions of northern Canada to the widely spoken Quechua of Peru, there are examples of polysynthetic, or agglutinative, languages. Agglutination is a linguistic process where prefixes and suffixes are added to a word to change the sentiment or exact meaning of the word. For example, in English we can add the suffix "s" to pluralize a noun, or the prefix "anti" to signify a contrary meaning. But in many Native American languages, a single word might have to be translated into multiple sentences in English, because so many affixes are added. As a brief example showing how complex this phenomenon can be for language learners, the word 'tuntussuqatarniksaitengqiggtuq' means "He had not yet said again that he was going to hunt reindeer" in the Inuit language.
So, we've seen that around the world there are several geographic areas in which languages are very hard to learn for English speakers because of linguistic, writing, and cultural differences. Asia, Africa, and the Americas are full of isolated ethnic languages and major international languages that can be a real challenge for Romance and Germanic language speakers. The hardest language to learn, in my opinion, would be one of the Eskimo-Aleut polysynthetic languages. However, not many people learn this language and it does not have a prominent global presence. Swahili in Africa is hard with its strange clicks and consonant combinations. But the hardest language to learn that is useful on a global basis is definitely Japanese.
As mentioned above, the Japanese language is difficult in its writing system, multi-syllable pronunciation, and complex grammar. But the true difficulties of learning a language are found in the study of the intricacies of the culture that profoundly influences the language. Learning to bow, nod, omit personal pronouns, and act with proper modesty can be just as challenging as learning the language itself. While it is almost impossible to know which world language is the hardest language to learn, Japanese definitely comes as close as any.