Simplethe lexical simplification list).
Up Goer FiveThis next one is too long to put in this post - but it's worth a read. The full comic is here: Up Goer Five (Or, right click on the image and open it in a new tab to view).
The style of translation in this comic is phenomenally difficult to achieve, even for humans. You can try it for yourself at The Up-Goer Five text editor. Most words have been substituted for simpler phrases, or explanations. Some technical terms rely on outside knowledge - which actually has the effect of making the sentence more difficult to understand. For example, one label reads: "This is full of that stuff they burned in lights before houses had power". This is referring to kerosene, which is highly understandable if you know of kerosene but inapproachable if not.
It would be an interesting experiment to determine the lowest number of words required to be able to produce this kind of simplification without having to draw on inferred knowledge (such as the type of fuel lights once burned). My guess is that you would need 10 - 20,000 before this became a reality. It would be difficult to automatically produce text at this level of simplicity. Explaining a concept requires a really deep understanding and background knowledge, which is difficult to emulate with a machine.
The above comic touches on an excellent point. If the words we use are understandable, does it matter if they're not the correct words? Previously, I have written about lexical complexity noting that many factors affect how difficult we find a word. The big factor that is played on here is context. For example the term 'handcoats' in the second panel is understandable (as gloves) because we know from the first panel that 'the sky is cold'. Handcoats is a word that you've probably never seen before, and out of context it would be difficult to get the meaning. This highlights the importance of selecting words which fit the context of a sentence. If the correct context is chosen and a simple word fitting that context is used, then the understandability of a sentence will be dramatically increased.