That's what I thought too but according to their latest quarterly report[1], ZenDesk generates revenue in Ireland, Singapore and "other" countries in Europe and Asia.

[1] https://last10k.com/sec-filings/zen/0001463172-19-000445.htm... (scroll up a bit to see geographic information)

I have no direct knowledge about Zendesk's use case however currency conversion is table stakes for any company doing international business. Purchase orders and employee travel expense reports being top of the list.