English is a bit weird when it comes to bagpipes: Even when referring to a single instrument, you commonly used the plural form, "bagpipes" (presumably because each instrument normally has multiple pipes; a chanter and one or several drones).
Klingon doesn't do this: DIron is grammatically singular when referring to a single instrument.
That being said, I can see how this can be somewhat confusing. Since it appears that saying "a bagpipe" is grammatically correct (although perhaps slightly less common), I've changed the primary translation to "A bagpipe is a windbag instrument.", although "Bagpipes are a windbag instrument." is also accepted.
I don't think I have ever heard "a bagpipe" used in English. However, per Merriam-Webster, that is an acceptable usage: