I think any slurring sounds are based on how a person pronounces them, IMO it's very easy to distinguish syllables in Chinese.

Anyways, Korean has words with the ending of "-ng" so if you hear that sound, it's Korean. Also, many Korean words end in consonants whereas all Japanese words end with vowels. Otherwise, there are words that sound an awful lot alike. For instance, the word "library" sounds pretty similar in Korean, Japanese, and Chinese.

I used to have a Korean roommate, so I can tell if someone speaks Korean right away because there are words that they use often (arusou, etc). But in music, sometimes it's hard to tell (especially if you aren't really paying attention).