Setting the primary language tells us a language you are comfortable using. For most people, this should be their native language. WYW uses this information to automatically set the "translate to" language in Google's translator. We expect that we will find other ways to use the information to make using our tools more effective for you.

Ultimately, how well you should know a word before adding it to your known list will be a personal choice. There are probably two extremes for acceptance. On the rigorous side, given the word in your native language, would you have come up with the word you are considering, without any other queues. On the more lenient end, can you tell the meaning of the word in the context in which it is presented. I tend to use the latter criteria. If I later find that the word is showing up as known, but it is not helping me understand the meaning of a sentence, I just pop it back into either the unknown or words being learned lists.

To us, words being learned are words that you would like to learn soon. They will likely be called to your attention when you look at the statistics of a media (movie, article, etc.) that you are about to enjoy. If you have an unknown word that is going to show up many times in your next web-based media, it would make sense that you would want to learn it quickly. If you are someone who can learn a word in one sitting, you may not find much use for the words being learned list. Otherwise, add a word to the words being learned list and it will stand out in future media, until you are ready to move it to your known list.