Hello,

I'm opening this discussion to find a song, which seems to be in french. Personnaly, I don't think it is because I am french and the only thing I can understand is a "très étrange" at times. But it is in french according to liming (french is also her mother tongue) who understood this : "mon ami un jour je passais très vite dans le ciel ~nanananana~ je crois que le ciel ~nananananana~ je suis fou avec le ~nananananana~ câlin ~nanananana~ je vous aime".

I tried to listen to the OST songs but I couldn't find it. Even Shazam don't know it. And trying to find it with so few lyrics is like looking for a needle in a haystack. If you want to listen to it, in the drama this song appears in episode 4 at around 13:50 (among other times).

Hmm it doesn't sound like it's being sung by a native french speaker, so perhaps a cover ? Or an amateur, french-language lover, who tried to write a song in french..
And it's 'un nuage passait' (or est passé) très vite dans le ciel btw
C'est "Je vous aime" par han seol hee j'arrêtais pas de la chercher puis elle est apparu dans mes recherches de spotify 
yep as haylam said it's Je Vous Aime by Han Seol Hee you can listen to it on mnet here:

http://www.mnet.com/track/16051271

(click the play/arrow button and it will load the player)

full “Sweet Stranger and Me OST” is this:

Kim Jong Kook (Turbo) – Idiot (바보야)
Henry – I Want to Enter Your Heart (니 맘에 들어갈래)
ZoPD, JeA – Want It (원해)
Junggigo, Dawon (WJSN) – Little By Little (소소하게 조금씩)
Lim Se Jun – Still, Love (그래도 사랑)
Solji (EXID) – You and I (너랑 나랑)
The Ade – When The First Snow Falls (첫눈이 내리면)
Lim Se Jun – Still, Love (그래도 사랑) (Acoustic ver.)
Lee Ji Yong (이지용) – Flying
Han Seol Hee (한설희) – Je Vous Aime?
Lee Ji Yong – A New Step
Han Seol Hee – Sunny Day, Rainy Love
Lee Ji Yong – My House
Lee Ji Yong, Jo Eun Ah – Try to catch me!
Lee Ji Yong – You And I
Lee Ji Yong – Can’t Stop
Oh Jang Hoon – Dancing in Love
Lee Ji Yong – Day
Great, mystery solved!!!!

Thank you, guys ^^