What Normmatt said. You can edit the relevant header entries to extend the RAM size, for some games it might even work. For most though you might find that it needed the space and will not work properly now, or may even get overwritten by something else.
Editing text in the binaries is horrible, as a ROM hacker working on the DS you hope you never have to do this (or in the overlays which have much the same problems). When it happens though I usually find there are three options, with a few more out there ones as well.
1) You do the full memory check, read, extension and more stuff. Really not fun but will work if you do it right.
2) Find some free space in the ARM binary. My favourite places to look at the wifi error strings in the binary, a game this early would not have wifi though. If there are wifi error strings then they might have it in several languages, generally be quite long and easily replaced by something more useful for you. If you have to break a bonus mode or something to have it fit then maybe consider that.
3) You edit the translated text to fit in the space you have, or help it fit in there by some means. Time to bust out the thesaurus if you are editing text (rather than using residence I might use home, or in your case rather than using appartement go with chez). You can cheat a bit here and maybe do things like dual tile encoding and multi character encoding. You can also go further and find that if a game uses say 16 bit shiftJIS then convert the decoder to use an 8 bit encoding instead. If you have repeated sections then maybe consider pointing to the same thing where you can.
The further option could be use the GBA expansion pack. It is present in DS mode and if effectively 32 megabytes of fairly high performance RAM if you want it to be, depending upon the flash cart you are using this might be more like 16 megabytes and might be read only if you have to use the NOR. Given you have all of about 4 megs on the DS none of those are especially horrible scenarios to my mind.
You could also try compression and decompressing it to free space in memory.
http://gbatemp.net/threads/unofficial-desmume-build-unused-memory-finder-tool.349332/ has something that might help with that (and 1) for that matter).
Thankfully I usually find it is only menus, maybe character names, some place names or something quite small that appears as text in the binary. Not always, and you have crazy things like Rockman EXE OSS that has everything in overlays (making over 1000 of things), but usually it is just small names and small pieces of text you can afford to mess around a bit.
