I am also not a native speaker, reading almost exclusively English ebooks, using the dictionary lookup a lot.
- You do not want to navigate with a D-Pad (Kindle, Gen3), it's too cumbersome.
- eink is preferrable, as the battery will last for weeks, compared to LCD (lasing only hours). It's also better on the eyes (for most people).
- If you still want to be able to load dictionaries of your own choice onto the device, you might consider the current Pocketbook models (forget the 302). However, they do not have a pearl screen (yet), there is one additional tap or pressing of a key involved (because of the user-interface), and the touch technology is wacom, so you have to get the stylus to use the touch function. With ths Sony, you just double-tap the word and that's it.
- The Sony lookup is the fastest available.
There is a lot of speculation going on about the new Sonys, they very likely will have wifi, but when it comes to reading and - especially - dictionary lookup: It already is as fast and easy as can be.
There are also some speculations about a next Kindle coming up, maybe with touch this time, who knows? This would give you the freedom of choice (of dictionaries) combined with the ease and quickness of accessing the dict. through touch.