How does this sound? "Words are the only unfalsifiable means of expression I know. Without them I can go through the day with a smile on my face even though I really feel like crying - so convincingly that I actually believe I'm happy." I think the dash works better in English: including the last phrase in the main sentence relates it more effectively to the fundamental idea: the dishonesty of pretending to be happy when you're miserable. The adverbial 'convincingly' brings out the action of smiling through tears; 'I'm' is more colloquial, which fits in better with the author's style, to my mind.