Yes ! Tax and Taxation systems differ from one nation to another., but not necessarily too difficult to understand!! As "complicated" as they could be seen, yet they are never beyond comprehension!
But they seems very complex because of the differing needs of different nations!!
While some are progressive others are not.
Some tax regimes are universal, when others are specific, where some target groups are covered. Taxes could be progressive where amount payable is progressive according to income magnitude!!
As " complex" as these could be; they are not beyond being understood in earnest!!