yes, and the answer is every so often

Many have removable filters that you're supposed to clean periodically. If there's nothing obviously removable in yours then it might have a "self-cleaning" system that would be harder to take out and clean yourself.

They do in Europe. They have water softeners too that you have to fill with salt. Don't believe it's the case around the world.

More than you ever wanted to know about dishwashers: https://www.youtube.com/watch?v=_rBO8neWw04