The detail I found most interesting was that the K4 actually has 6 language options, and that when it shipped several weeks ago, it came with full support for English (US/UK), French, German, Italian, Spanish and Portuguese. And I don't mean that the K4 has menus in these languages; Amazon have already written and released user guides and other docs for each language. There's even a localized onscreen keyboard for each language which offers the appropriate custom characters for each language (scroll down for screen shots) as well as a dictionary.
Clearly Amazon are planning ahead for the launch of several local Kindle Stores. The language options make it pretty damn clear that the K4 will be the Kindle that Amazon will offer in each of the new markets. Of course, Amazon might also offer the Kindle touch, but I won't know for sure until it ships.
To be honest, this isn't that much of a surprise. It's common knowledge that Amazon plan to launch Italian and Spanish Kindle Stores, so the language options are really just confirmation of what we already guessed.
On the other hand, the Brazil option was a little surprising. I had gotten a hint here and there that Amazon planned to enter that market, but all the hints I heard were vague and unconfirmed. This is the first real proof that Brazil is one of Amazon's next targets.
BTW, I'm fairly certain that the Portuguese language option is intended for Brazil, not Portugal. That's why the country name is included as part of the option. If the K4 offered an English (Australia) option, I would reach the same conclusion about that country, too.
The language options also give us a hint as to time frame for when the local Kindle Stores will launch. If Amazon plan to offer the K4 (and not the next Kindle) in new markets, then it would seem likely that the Spanish, Italian, and Brazilian Kindle Stores will all launch in the next 6 to 8 months. My guess is based on the assumption that Amazon will launch a new Kindle next year, and the event will happen some time between August and October.
Update: I've been reminded on Twitter that Amazon launched Amazon.es a few weeks back. This is true, but they didn't launch a Kindle Store.
Click on the screenshots below to enlarge. Note the keyboard options.