Regarding the software language issue, when you first boot the computer, you will be asked for the default language in which you want to operate. This is similar to most other OSes -- you get a screen with all the supported languages listed in their own native script, and you pick one.
Every copy of OS X includes the ability to operate in any language that OS X supports -- it is not sold in local versions, aside from packaging or other trivia (like the instructions on this one screen might be in Japanese and have Japanese pre-selected as the default choice if you buy it in Japan, but English will still be on the list, and will work fine, once you select it).
After that, in the International pane of preferences, you can define a list of all the languages you are interested in using, and order them. Whenever you start a program, it will examine this list, and it will operate in the highest language on the list that it supports, or else whatever other language it does support, if no supported language is on the list.
So if I close Adium, change my default to French and run it again, the menus and options will be in French. If I set my top language pick to Japanese, and run iCal, it comes up with Japanese menus.
But if I run an app that does not have localization packs in it, such as Deer Park Alpha 2, then it always runs in the installed language (English in this case). So any software you buy that is *only* localized in Japanese, for instance, will always run in Japanese, and only Japanese, whether or not Japanese is even on your list.
Finally, some apps support localization to some extent, but not using Apple's system. Microsoft Office 04, for example, when purchased in the U.S., has Japanese language features, but is also sold in localized versions in various countries, and does not support multiple localizations, AFAICS, at least in the US version.... This last class of apps is the one that may be problematic for you.
