My apologies that was a rushed response.
8 bits are used but as that is just about enough to fit the kana, a roman alphabet and what appears to be a heart you need more info for kanji. The usual route is to only take what you need and hope but for the more inventive/lazy you can up it to 16 bits which amounts to 65536 characters: more than enough for just about every language going.
Conventional relative search takes one 8 bit string and then checks the next string to see if it is a value acceptable (think a=1, b=2 c=3) wanting the line acb and seeing 132 or more accurately a number with a first digit a second 2 higher and the last with 1 above the first or 1 below the last means there is a good chance you have the string responsible.
Unfortunately most games as already mentioned now use 16 bits to represent a character and as the old tools are geared for 8 bits it falls flat on its face.
Thus you need to find a relative searcher capable of 16bit intervals which again may be a problem as some games use 00 to end a line (8 bits) but if you can get it you should be OK.
At next reply yeah breakpoints and brute force, it is not glamorous but it works.
The file system (strictly it is a deconstructer, decompiling refers to turning binary code to high(er) level code), check the link in my signature about DS rom rips and enhancements for basics.
Also ndsts
http://www.gbadat.altervista.org/tools.htm
ndstool (frontends include DSlazy and DSbuff)
Or you could even grab by hand:
http://nocash.emubase.de/gbatek.htm#dscart...roromfilesystem
IPS: international patching system (or something similar). It is an old patching system common in everything up to the n64, it only does files up to 16 megabytes though and it works by having an address and changing that. You shift the code but change nothing and the patch making app sees massive changes and makes a massive file. Therefore IPS is no longer used. Popular alternatives include xdelta, PPF, custom made patching types/tools and BSDiff (a lot of trainers other than those by cracker and bleep and patches from release groups use it).
ARM: (I do not recall mentioning it but OK) the type of processor the DS has. It has an ARM7 and ARM9. See the link I gave for the DS file system by hand for (much) more.
ASM: short for assembler/assembly. Binary is what the machine runs and source is what the developer makes. It normally refers to diassembled code where the binary is made to look nice to human eyes and the creation of code to be assembled.