I continue to be amazed about how many people believe that Drupal 6's localization (l10n) and internationalization (i18n) improvements aren't a killer feature.
Time to beat some sense into the nay-sayers: according to the CIA's factbook, only 4.84% of all the people in the world have English as one of their native languages. While it is believed that one out of every five people on earth knows some English (but not necessarily much), the fact remains that for more than 95% of the people in the world, English is not the main tool for communication, nor is English part of their cultural identity.
Admittedly, I knew that l10n and i18n improvements weren't going to be compelling for a large portion of our current install base, but I placed my bets, and wanted to see this happen nonetheless. That is exactly why I made Gábor a Drupal 6 branch maintainer.
I learned that every time we release a new version of Drupal, Drupal attracts more users. In other words, making a better product translates to a bigger install base. Every major Drupal release asserts this observation. It took me a couple years to realize that it was actually that simple a formula. Thus, I'm confident that the l10n and i18n improvements in Drupal 6 will convince many more people to use Drupal.
Also, Drupal isn't a panacea, but I'd like to believe that the l10n and i18n improvements in Drupal 6 could mark a small but important step to make a positive change in the lifes of folks in remote parts of the world. I'd expect that NGOs (like Greenpeace or Amnesty International) -- or even the NATO -- take interest in seeing Drupal's translation community flourish.
So if you want to learn more about the l10n and i18n improvements in Drupal 6, or how they compare to those of other Open Source CMSes, I'd encourage you to read Gábor's master thesis (PDF, 650KB, mirror) or to check out DevelopmentSeed's comparison chart.