For magazines or books, how much does "text volume" differ when comparing Chinese to English or German?
Judging from my personal experience (I do translation for a living), the English and Chinese versions of a text have a word count ratio of about 2:3. That is, if the English version has 1000 words, the Chinese version will usually have about 1500 characters. 

However, the Chinese version usually takes up less space. In Microsoft Word, with the same font size and style, the Chinese version is usually one third shorter than the English version. If the Chinese version has 10 pages, the English version will usually have 15 pages. 

This may seem to be a paradox, but please note that Chinese texts are counted in characters, not words. Each Chinese character consumes the space of about two English letters, while an English word is five letters long on average. 

Of course, these numbers vary every time, depending on what and how you translate. They are just very rough numbers to give you a general idea. :)