And it only took a brand new version of DesMume to get it working.
Here is the full rigmarole of getting this to work under emulation (for those that don't need to run stuff from no stinking flash cart).
Download the latest release of DeSmume, from the link above and don't extract it, simply copy it to a folder of your choice (ours is simply called unzipped)
Locate your Rom by the time honoured traditon of googling its name on google. Saga2 Hihou no densetsu
We'll throw you a bone here by directing you to rapidlibrary and put in the name there to see if its up on any file drop places. ( and for gods, sake ignore all the weird porn requests that people make there).
With the rom downloaded to a folder of your choice, go to the Crimson Nocturnal sub page and download the patch from the list of filedrops provided and extract it to the same folder where your SaGa rom is located.
Play the Rom image in DeSmume and see if the main title screen appears, if it does open up Xdelta from the Saga2 translation patch file and close the emu. (You'll get a warning screen in japanese if you use any other emulator to patch this at present either that or it just won't work.)
In case you mess up make a copy of the rom and then with Xdelta open add in the directory for:
*where the patch is for patching.
*where the rom image is for patching (easy both should be in the same place)
*the new name for you rom file with .nds at the end of it.
THIS BIT IS IMPORTANT OR THE PATCH WONT BE RECOGNIZED.
Press apply and it should patch ok, run Desmume and see if the title screen is in English. If so well done you've patched Saga for emulator play.