He hides his sorrow behind a smile.
- Il cache sa tristesse derrière un sourire.
He was attracted by her smile.
- Il était attiré par son sourire.
He grinned with delight.
- Il fit un large sourire de satisfaction.
That person has had an odd grin on his face for a while. What do you suppose is behind it?
- Cette personne a eu un étrange sourire sur la figure pendant un instant. Que pensez-vous que cela cache ?
She approached him with a smile on her face.
- Elle lui fit des avances, un sourire aux lèvres.
I saw a joyful smile on his face.
- Sur son visage, je vis un joyeux sourire.