You must be an EU citizen. You must get an EASA ATPL. You will probably need to buy a type rating in an A320 or 737. And then you aren't gonna get paid much money for a while. I work with a lot of European pilots in the Middle East and few of them plan on going back because, coupled with high taxes, pay is low in most cases. As for Ryanair and a few other LCC's, their multinational basing created huge tax headaches that might make it very difficult to ever take advantage of all that "free" stuff the people in the EU get for their 40-50%+ taxes like pensions, free health care, etc.

I can't give you specific details on a specific country or airline but guys from Ryanair, Easyjet, Aegean, Czech, Wizzair, and others all tell me the same things pretty much every time I fly with them and few if any plan to ever go back to Europe. I can't say that's an enviable career path from the standpoint of an American citizen who can choose between many airlines with many possibilities of places to live, considering reasonable commutes.

If you're an US citizen and you are contemplating this, you are about to make aviation much harder, expensive, and less rewarding than you realize.