I think the English of the average American is worse than that of the average German. I've always found that a bit funny.
I was reading something from DevkitPro a while back, and I think I remember the way the microphone is handled to be a bit odd. Is there a maximum length limit? (Is there a limit in DSLinux?) It's sad that there aren't more homebrews that use the microphone.
To answer the topic question:
NitroTracker has a fairly good voice recorder, for up to eight seconds. You can then overdrive it to 500% so you can actually hear it.