If the anime I've been watching for almost a decade has taught me anything, it's that for Japanese at least, the clues behind sarcasm there and in English aren't quite that dissimilar. Tone of voice can still be used, you just have to be a bit more careful about it. Sometimes it just comes down to accent or word choice. After Googling, the consensus seems to be that sarcasm really comes down to the shared context in the conversation. If it's obvious and you both get the joke, the sarcasm worked. It's just as easy to miss sarcastic comments in English -- as not everyone says it with the same verbal emphasis. And of course, we can always understand sarcasm online. </sarcasm> (Okay, that was a poor joke... moving on...)