Word for "device that provides constant doses of a liquid/dust/substance"

The word “dispenser” does connote that the amount dispensed is measured and consistent. I think it may, in fact, be the word you’re looking for.

It probably doesn’t carry that meaning as strongly as your original word, but I don’t know of another English word that would serve that purpose any better.

How about regulator, per Wiktionary:

A device that controls or limits something.

I can come up with a few: Doser... Meter (from the verb "to mete", but might be too confused with the measurement).

I think Dispenser is accurate, actually. They usually dispense one unit of stuff at a time, e.g. one pill. Is there another word in Bulgarian for dispenser vs. "dosator"?