Most of the posts I see on HN mostly revolve around learning languages. In my opinion that's only part of the problem. It's more difficult to get the structure of sentences and tenses correct. I personally know words in 2 - 3 languages which share a root with my mother tongue, but it doesn't mean that I can speak those languages because I often don't get the way a single word transforms based on the tense, part of speech etc. For eg. merely knowing the word "smile" would only take you so far. Knowing the difference between "He is smiling", "He smiles", "He keeps smiling at me" is the tricky part.
Perhaps we are obsessed with learning words because it's the easier problem to solve. Learning sentence structure and grammar takes time and effort.