What indicates that "les" here is a plural? I don't understand why i give lessons are accepted, but i give lesson not....
Actually "les" is uncountable here, which is why it doesn't have an article ("een les"). "I give lesson" is simply not correct English, and "I give a lesson" has a different meaning than the Dutch sentence.
But since this is the separable verb lesgeven, the uncountability of les doesn't matter, since it's not an adjective, right?
Is "I give lessons" really the same as the alternate translation, "I teach"? For example, at least in English, one could teach their dog to sit, without "giving lessons" per se.