Last night, a YTN story offered up this monstrosity, which made me pause the clip to work through: 특정경제범죄가중처벌법상 (Specific Economic Crimes Aggravated Punishment Act). I think that if Korean used the Roman alphabet rather than hangeul, it would come in for the kind of ribbing that German does. The syllabic blocks make compounds look more concise, but in Revised Romanization this would turn into the gobsmacking teukjeonggyeongjebeomjoegajungcheobeolbeopsang.

Wow this is a great question. I think Hailey is right, but there are some other words that could be considered 'challengers'. Here are a two I found searching through the dictionary: 고운점박이푸른부전나비- Scare Large Blue Butterfly. The Korean term actually means something like "pretty spotted azure butterfly". Not quite sure what 부전 is, I think it's the family of the butterfly. 모시금자라남생이잎벌레- Aspidomorpha transparipennis. I'm not sure if there is an English name, but it seems to be a type of leaf beetle. Again the Korean term is descriptive. 딱다그르르딱다그르르하다 is a sound mimetic word that as you can tell, has 딱따그르르 repeated twice to describe the sound. In English compare something like 'drip-drop' to sound mimetic words (though of course this word has a different meaning). The 하다 meaning "to do" adds on an extra two syllables which may help this word win. On the other hand, this word is somewhat North Korean, and if you are going to include North Korean words there are some very long combos that result from fusing all the syllables together (For instance the title of some government organizations or conferences). On the other hand, the words I listed (there are more like them) are all the names of various animals or plants. So, you could disqualify my words on that account. Anyways, I just wanted to add a bit more to this answer, since I thought it was interesting!

딱다그르르딱다그르르하다. If you drop marbles and those stuff roll down the ground, you can say they do 딱다그르르딱다그르르 We can get it even though it's a North Korean word.