If you pack your bags and take a trip to South Korea, you will have no idea what anyone would be trying to say to you. Looking around, all of the signs would be in Hangul instead of the somewhat comforting Latin alphabet and you would be lost.
When two people can not understand each other’s writing or speaking systems, they are speaking different languages. If you were in South Korea, this would unarguably be the case.
Mutual Intelligibility is the linguistic term describing when two speakers speak the same language. It’s defined opposite of the above scenario, two speakers understand each other.
If you instead packed your bags for the United Kingdom, people there would speak different than you, but you could easily understand them. Mutual Intelligibility allows for some wiggle room in terms of colloquialisms, pronunciations, etc.
What may surprise you is that oftentimes the line between languages is not always as clear cut. For example, Chinese is often called a language, but is in fact a collection of languages. The speakers of Mandarin Chinese can not at all understand speakers of Cantonese and vice versa. Speaking, there is no mutual intelligibility and so one would label them as different languages.
The tricky part comes in terms of writing. Standard Simplified Written Chinese is the same regardless of which variation you speak. This means that if someone from Beijing (where Mandarin is spoken) travels to Hong Kong (where the people speak Cantonese), they would not be able to converse with anyone on the street, yet they could write down what they wanted to say and be perfectly understood.
Something similar happens in communities that use sign language. While someone with hearing loss from Melbourne, Australia could read the New York Times without issue, they would have no idea how to communicate with someone from the United States. American Sign Language is completely different and unrelated in any way to Australian Sign Language. Similar to the situation in Chinese, a singer from Sydney that flew to Fort Worth would need to write down their message to be understood.
Other problems arise with regional variations among languages. Dialectal Continuums pose major problems for those trying to put boxes and label the “languages” of the world. Take German for example, specifically the northern dialects known as Low German.
Anyone from Antwerp or could understand someone from Brussels, and anyone from Brussels could understand someone from Munster. A businessman from Munster could call up his stock broker in Hamburg and tell him to sell all his shares without problem. And that same stock broker could take the evening train home to Berlin and speak happily with his wife.
If that wife tried to talk to someone from Antwerp, however, she would find it incredibly hard to be understood and to comprehend what the Antwerper was saying. Dialects are similar to their neighbors, and so going a city over is no big deal. Yet the farther one travels from their home, the more difficult it becomes to converse. Where exactly does mutual intelligibility end?
Problems like these are common in Africa and South-East Asia and other parts of the world and are what is responsible for the huge range of possible languages in the world (6000 – 7000).
What dialects are called one language vs. different languages is often the result of politics. Pakistani Urdu speakers can effortlessly talk to Indian Hindu speakers, yet they are different languages. Before the breakup of Czechoslovakia the official language was Czechoslovakian, but after the breakup, there is the Czech language and the Slovak language.
The lines between different languages are incredibly blurry. Grouping methods of communication into small boxes for political or cultural purposes obscures or ignores their complexity. Where someone stands on what is or isn’t “their langauge” reveals more about their world view than their understanding of phonology, morphology, or syntax.