"He is always sad, and he doesn't know how to smile."

Translation: Il est toujours triste et il ne sait pas sourire.

[Faroyd21]

Bonjour! Dans cette traduction, on ne peut pas dire "Il est toujours triste et il ne sait pas comment de sourire" ? Merci

[Jojo553168]

That would be il ne sait pas comment sourire. (no de)
But, it would be a bit different, it would mean he needs to learn how to smile technically. The original sentence just means the person never smiles.

[Faroyd21]

Thanks :)

[Tmrsk5]

I got emo guy for this sentence. Gold star for Duo!