To change the language on a Nintendo DS please see the instructions below;
Start up the Nintendo DS
Before going into the game use the stylus to click on the icon that looks like a little DS at the bottom of the screen
From here you should see a pink icon that looks like a spanner. Select this using the stylus.
The you should see another pink icon that looks like a globe. Use the stylus to select this.
The next screen you come to should allow you to choose your language. Highlight your desired language then press A to confirm.