Princess Toadstool pronounced it in the television show /ˈlækiːtuː/ (la-KEE-too)
http://www.mariowiki.com/lakitu
As that page states and if you ever watched the show you would have heard this being used, but like it says "(la-KEE-too)" is western
It maybe pronounced different in other regions
If you are looking for official I'm guessing this is one of the closest you'll get because it was spoken/pronounced like this in an official production of a Mario title