Unpack and repacking the isos can be handled with a few tools.
I quite like wii scrubber
Others like wiimms iso tools https://wit.wiimm.de/
Popular compressions and formats used for storage within wii games include u8 (u8tool is then good stuff), szs and yaz0.http://wiki.tockdom.com/w/index.php?title=List_of_File_Formats
if for mario kart but some apply to other games.http://wiibrew.org/wiki/File_formats
has some more.
Text itself. Can be coded any way the devs wanted, and they had all sorts of things they liked doing for the wii. To that end unless someone has gone before on this game or a sequel/prequel, maybe something from the same dev, you are on your own. Some will be in graphics, some basic text a like formats, others will be pointers and normal ROM hacking fare and others will be a mess of assembly and control codes. That said displaying text does not vary much in underlying theory between any system really so all the guides covering tables, formatting and such will apply here as well, obviously something going incredibly in depth on pointers in the snes memory layout will not directly apply but understand pointers there and you will not struggle elsewhere.