This is a sign from a pub. I would expect it to read “Irish truth” or “true Irish”. Why is “Irish true” used?

sign


Solution 1:

This is an advertising slogan, not a considered argument, so it could be simply that 'Irish true' rhymes with 'Irish Dew'.

Solution 2:

Part of the answer is that it's an advertising campaign trying to brand a product as distinctively Irish. Ireland is historically noted for good whiskey.

I think they mean authentic from an Irish viewpoint or quintessentially Irish just as a leprechaun is Irish true but a Viking isn't.