Luckily, OALD is available online:
civ•il•ized (BrE also -ised) /'s{I}v{shwa}la{I}zd/ adj.
1 well-organized socially with a very developed culture and way of life: the civilized world * rising crime in our so-called civilized societies * civilized peoples
2 having laws and customs that are fair and morally acceptable: No civilized country should allow such terrible injustices.
3 having or showing polite and reasonable behaviour: We couldn’t even have a civilized conversation any more.
4 typical of a comfortable and pleasant way of life: Breakfast on the terrace—how civilized! * Let’s go somewhere civilized and have a meal. opp uncivilized
Note the stuff in red near the beginning. That's how dictionaries often indicate an alternative spelling.
Now, what are your other two dictionaries? This is fun.
But their first spelling of choice is also with a "z". My other dictionaries are Engelsk-Svensk ordbok from Svenska bokförlaget Nordstedt, 11th impression and Engelsk-svenska/Svensk-engelska ordboken from Esselte Studium, edition unknown, since the first pages are missing.
But that doesn't matter. What matters is how Oxford Advanced spells it, and that is the 3rd edition, 11th impression. Not my fault if the British English has degenerated since I went to high school.
Your problem is that you aren't civilised enough, and thus lack in reading comprehension. The above quote
is from the Oxford Advanced Learner's Dictionary, the latest edition.
The Esselte and Nordstedt ones are poorly researched dictionaries, aimed at (Swedish) kids and laymen, and intentionally omit everything complicating anything. I can understand why they appeal to you, but you should rely on a more widely recognised dictionary. OED is a bit expensive, but the Merriam-Webster 3rd Ed should be affordable, that is, if you can handle the preference for anything AE.
As for me, I own more dictionaries than you do, a couple of grammars and thesauri, a fair number of style guides (from various publishers around the English-speaking world), and also quite a few general-interest books on the English language. Practically all of them bring up the subject at hand, pointing out the British preference, but some also highlight the fact that there are at least THREE distinctive ways to handle the "ize" words.
Of course, a number of dictionaries are available online, free of charge, among them your beloved OALD. A simple Google search will tell you more about how the spelling varies on different sides of the Atlantic Ocean, but you could also ask around here. Several writers and at least one PhD, at your disposal. If you ask nicely.
So please, child, don't embarrass yourself further.
phobia.