How can I express 입에 착 감기다 in English?
When I say something, its pronunciation or spelling is so fluent that I can speak softly and rhythmically
In this case, I would like to say 입에 착착 감긴다
How can I express this in English?

이건 말할때 입에 착착 감겨서 좋다

Question

How can I express 입에 착 감기다 in English?
When I say something, its pronunciation or spelling is so fluent that I can speak softly and rhythmically
In this case, I would like to say 입에 착착 감긴다  
How can I express this in English?

이건 말할때 입에 착착 감겨서 좋다

Answer

Maybe "roll off the tongue" or "feel right on the tongue".

"입에 착착 감긴다" => It rolls [trips, slips] off the tongue / It feels right on the tongue.

"이건 말할 때 입에 착착 감겨서 좋다" => What's good about it is it rolls off the tongue / It just feels right on the tongue.