Yep, you are right. The language in the OS is included in letīs say extra language folders, mostly in two main folders OEM and SYS, and build for every program folder.
(0407 - folders containing german language files)
If you want the programs in another language, you have to cook your own rom. You take your prefered (swedish) language rom and copy all folders from OEM and SYS to another rom with the progs and stuff you want to have.
So, take swedish rom, extract it with kitchen, copy out the three extracted folders (OS, OEM, SYS). Then extract a prefered program rom (wwe) and delete the specific language folders. Take instead these, that you got from your swedish rom (have a look in the copied folder) and put them in the SYS and OEM folder, in that way that they match to the programs.
Last step, is rebuild your shiny new swedish rom and flash it - thats it....
So the OS supports the swedish rom but does not contain the lang. files. :P
HTC Touch HD