Why wouldn't it be 듀올링고? Because one ㄹ indicates more of an "r" in Konglish...
Either add a Koren Hangul keyboard to your device (Windows; Settings; Languages, etc), or type in Latin alphabet transliterations of the Hangul characters that you would use (e.g. Duolingo = d yu o l i ng g o)
Duolingo + Korean = Douringo! This is why there are so many Asian "r" "l" stereotypes.
Shouldn't it be 듀올링고? As far as I know single 'ㄹ' between vowels is more similar to 'r'
I think it's just a way to let you practice using the alphabet with words you already know.
To help learn the script. In order to read Korean quickly you have to be able to instantly recognize many syllables, so this is just to help you learn them.
I think its also part of the korean grammar. Even if words are in english, theyre teaching you how to say it in hangul so you wouldnt sound robotic when speaking in full hangul. You can notice this change when you watch some korean variety show.