I would say the degree of coverage of pre-war vs post war is about the same, but now there is a lot more detail. The number of pages has increased from about 220 to about 250. No colour in the 1st edition, a bit in the 2nd, and plenty of guns in colour in the 3rd, especially the pre-war pistols, the pictures of which have also been enlarged. There is a new section on pellets, well illustrated in colour, but all immediate post war. All in all, a much nicer book to browse through, certainly far better than the 1st, and better than the 2nd .
Language need not be a problem with foreign airgun books these days. With a smart phone and a good app, (I have a Pixel 3a, which comes with Google Lens), I can take an instant translated picture of any page, complete with the illustrations, all in the right place and the fonts well matched to the original, and I can then print it out if I want.
(You don't even have to tell the app it what the language, as it works it out for itself. The app has been excellent for me with Czech and Polish airgun books).