I’d say it’s not ‘very’ popular anywhere outside of the Pacific. The USA has the most kava bars and we probably consume the most kava of the non-pacific island countries...but it’s a big highly populated country, so most people still don’t know what it is. Other than the ‘real’ kava drinkers here, a lot of people might have a vague familiarity with the name kava, and probably think of it as a capsule or tea bag you’d buy at the nature/herb store.
New Zealand is worth a mention too, although...it’s technically a pacific island. There seems to be a handful of drinkers in a lot of countries, but there’s definitely more from a few certain ones. — I think KapmKrunk might have some stats on the KavaForum visits...that data could give a pretty good clue to the popularity ranking by country.