Tiger, like previous versions of OS X, is multi-lingual out of the box. Your language of choice can be set in system preferences.
However, if by "upgrading" you mean you want to use Tiger installation disks that came with your powerbook to install Tiger on a different machine, that's a bad bad idea. First of all, it's illegal. Second, The OS installation and software restore disks that come with Apple computers are machine specific, that is, they are configured to run specifically on that machine. Using those disks to install OS X on another machine will almost certainly lead to problems, assuming you are successful in getting it installed in the first place.
The retail version of Tiger is significantly different in that it is configured so it will install on any Apple machine that meets the minimum hardware requirements for using the OS.
