That must have been a challenge to dub. In the original Bart is speaking English, not Quebecois French. So, when Bart is speaking Quebecois French he must have really leaned into the accent to make it believable that the policeman didn't understand.

Here's the original for comparison:

https://youtu.be/EUSGPubsxcM?t=93

It's funny because in the original the policeman is the only character in the scene with a decent French accent. The two criminals sound absolutely horrible.