score:34
Mein Kampf was illegal in a lot of countries for a very long time.
As already noted in a comment, it was never illegal in Germany. You could sell and buy any existing copies. Reprinting it was not allowed by the copyright holder (the German federal state of Bavaria inherited it from Hitler after his death).
The copyright expired 70 years after Hitler's death and so reprinting it is allowed again. Germany decided that instead of leaving the reprinting business to a lot of private right wing organizations, the "Münchner Institut für Zeitgeschichte" (Munich Institute of History) published a version that contained the original print accompanied by a comment: "Hitler, Mein Kampf: Eine kritische Edition"
Except for illegal reprints, anything printed between 1945 and 2015 are probably books that feature excerpts, comments and texts by other authors. But again, the book itself was never "illegal". Existing copies could always be sold, bought and read freely.
Upvote:7
There's some indication that the English version circulated in the late 1930's deliberately omitted or reduced Hitler's anti-semitism and aspirations on Europe.
US Senator Alan Cranston had read the German version, and found an English translation in Macy's Bookstore in New York in 1939. On browsing he noted it was too short and too light, and had significant differences. So he and a friend worked to publish an "anti-Nazi" version of the book in English.
“I wrote this, dictated it [from Hitler’s German text] in about eight days, to a battery of secretaries in a loft in Manhattan,” Cranston told the Los Angeles Times in 1988. They produced a tabloid edition of 32 pages, reducing Hitler’s 270,000 words to 70,000 to yield a “Reader’s Digest-like version [showing] the worst of Hitler.”
Further info from Los Angeles Times archive, dated 1998-02-14
So depending on the source, you might indeed be reading a deliberately-altered version, beyond the changes that plain translation would produce.