ㄹ has three pronunciations: 1. L 2. R (Not the English one, it's close to the Spanish one but you have to flap your tongue only once. In some American accents, they make that sound too. For example in the sentence "I did it", the last "d" in "did" is prounounced in a way similar to the Spanish R) 3. N When to pronounce it as L? -at the end of words: 말 mal, 술 sul, 제발 jebal -before consonants: 울다 ulda, 말하다 malhada*, 슬쩍 seuljjeok -after another ㄹ: 몰래 mollae, 멀리 meolli, 들리다 deullida When to pronounce it as R? -before vowels: 둘이서 duriseo, 버리다 beorida, 달아오르다 daraoreuda When to pronounce it as N? -after ㅇ: 능력 neungnyeok, 강렬하다 gangnyeolhada*, 승리 seungni -after ㄱ (and ㄱ becomes ㅇ): 격렬하다 gyeongnyeolhada*, 식량 shingnyang, 박락 bangnak -after ㅁ: 함락 hamnak, 첨력 cheomnyeok, 심리 shimni -after ㅂ (and ㅂ becomes ㅁ): 입력 imnyeok, 감사합니다 gamsahamnida, ~입니다 ~imnida At the beginning of a word, you can choose either L or R, many Koreans find it easier to say L, but R is the most correct one in my opinion. 라디오 ladio/radio, 레몬 lemon/remon, 라면 lamyeon/ramyeon Then we have ㄹㄴ and ㄴㄹ, I wanted to explain this separately. ㄹㄴ is always pronounced ㄹㄹ: 물노리 mullori, 잘나다, jallada, 별나라 byeollara ㄴㄹ is MOSTLY also pronounced ㄹㄹ: 곤란 gollan, 말란하다 mallanhada, 진리 jilli But there are some exceptions! In some words ㄴㄹ is pronounced ㄴㄴ (정신력 jeongshinnyeok) but you'll have to learn those by heart, they're mostly compound words that are rarely used. And finally, I wanted to say something about the words with a * (말하다. 강렬하다, 경렬하다). In spoken language, the ㅎ is often ignored when there is a ㄹ before, turning the L into an R. Korean People will spontaneously pronounce those words as marada, gangnyeorada, gyeongnyeorada, etc. Korean pronunciation is complicated, right? :) Don't hesitate if you still have questions about this (or something else).

It's only pronounced as ㄴ during sound changes, after a few select sounds :)

Complete list of pronunciation rules due to sound changes: https://en.wikibooks.org/wiki/Korean/Advanced_Pronunciation_Rules