One thing I often forget is that Wikipedia isn't a single collection of enclopedia entries, or "articles". Rather, it is a collection of collections of articles; the English-language version of Wikipedia is entirely different from the German or French versions. Each article is written and maintained by people proficient in that language, and there is surprisingly little overlap among various Wikipedias.
Take the topic of light pollution, something I am aware of every time I travel from my home in the boondocks where there are no external lights on at night to big cities where the beautiful Milky Way can't be seen.
The coverage of this topic is entirely different in the English, French and German; even the depth of the articles varies. Here are the tables of contents to the three Wikipedia articles on light pollution, all auto-translated into English for comparison:
The info pro who told me about this is in Canada, where she often needs to search in both French and English. One more reason why I find professional conferences so valuable -- I get so many new perspectives!