Since I will become a senior in the coming fall semester, I guess this is one question I have become more informed about compared to my time as an innocent freshman. I do get quite some questions about this too, so I hope this post can help you a bit more in making your decision to come study in a Korean university.
Some basics you need to know about working in Korea before we start:
Local Korean companies vs Multi-National companies
For local Korean companies, they would definitely require Korean proficiency. And when I say Korean proficiency, it is not 반말 (the form of informal Korean you use with your friends), but formal, business Korean. So if your aim is to work in Korea, in a local company, you definitely have to be able to speak Korean well.
*Note: Korean multinationals like Samsung or LG are not really in this category
The number of multinational companies that choose to locate in Seoul has been increasing over the years, and Korean multinationals such as Samsung are becoming well-known brands worldwide. In this globalizing context, such companies have two tracks of employment. One would be the local track where they are looking for Koreans to work in local branches and contact with local clients, and the international track where they are looking to send employees overseas or back to their home countries, or deal with international clients. For the local track, it is the same as Korean companies – Korean proficiency is needed. Korean proficiency is not always needed for global track.
However the international track is becoming more and more competitive due to its better employee benefits and the opportunities for overseas posting. Also, working in the more global departments in multinationals gives one a higher chance of escaping from the strict hierarchy in local Korean companies, so many overseas Koreans are very interested and definitely well-qualified for this track as well. They are effectively bilingual in English and Korean, so they have an advantage over other applicants who only speak one language. So I cannot begin to stress the importance of Korean proficiency if you intend to work in Korea. Korean proficiency would also be an added bonus if you want to work in Korean multinationals as well, even if your aim is to be posted back to your home country.