"He can speak five languages."
Translation:Il peut parler cinq langues.
"Il parle cinq langues" = "he speakS five languages". "Il sait parler cinq langues" = "he CAN speak five languages"
actually il sait parler doesn't mean he CAN, it means he knows how to, and this is the sort of thing DL often insists on, since we are learning how to use the words.
The sentence makes sense and I would guess here that the meaning is similar to "Il sait..." (not a native speaker so not sure). But for other verbs, the meanings can be different. I remember my French teacher saying "Il sait jouer au tennis" means he can play tennis because he knows the rules, etc., but "Il peut jouer au tennis" means he is physically able to play.
I've noticed that when there is a number, the article falls away. For example, "je mange six pommes".