"Internationalization means externalizing the user interface so the software can be translated."I've been in i18n* for over 25 years, and I haven't seen this assumption change in that time. So why is it a myth? Think about why people or companies buy software. Do they buy it for the user interface? If someone in Japan sees email software with a Japanese user interface which can only send and receive email in English (US-ASCII), do you think they'd buy it? Of course not. People buy software to do something to their data. If the software doesn't do to their data what they want/expected, then they're not going to buy it. Seems pretty straightforward, but what does this have to do with internationalization? The answer is, internationalization is, first and foremost, adapting the data processing to handle data from all over the world. This is far more essential than enabling the user interface to be translated, and a good deal more difficult. The difficulty lies mostly in the planning and design, or rather, getting it into the planning and design. The implementation is only difficult in getting implementers to learn a few things and then execute with those things in mind. Externalizing messages is a piece of cake (don't forget images and sounds).
* see Norbert's blog