Getting a visa in Korea is not an easy task, so even the smallest nuances are important here.
In the infographic, you can find detailed information on when it is necessary to confirm knowledge of the 
Korean language, and when submission of such documents to the immigration office is not required.
 

The infographic also provides a list of documents that are accepted as proof of knowledge of the Korean language. 
Please note that the results of the KIIP preliminary test and the TOPIK exam are valid for 2 years from the date of 
announcement of the results. This period also applies to other documents confirming knowledge of Korean.

In addition, many people do not know that with proof of knowledge of the Korean language, the period of stay is often extended 
for a longer period compared to those who do not provide such documents.

See the full post, study the infographic, and if you have any questions, feel free to write in the comments. 
I will try to help!