It's a matter of common sense. Let's suppose you come up with a strong idea, great prices and cutting edge marketing. What's the point of being smarter, faster, cheaper and better if there is a chance your clients may not fully grasp the message?
It's a matter of courtesy. You're the one who's supposed to reach out to your clients, not the other way round. Speaking their language is part of treating them well.
If you've never tried a machine translation, we recommend it — just for fun, because the hilarious results will bring you right to us!