My main hobbies on Wikipedia include fixing typos and spelling errors, adding inter-wiki links, and adding links to the same article in other languages I know. If I ever have time one of these days, I may try to improve some English articles by adding information from the corresponding articles in other languages.
Wikipedia as a Translation Resource
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I believe that Wikipedia is the best online source of individual word translations (provided you already know the language to a certain extent) because you know that it is up-to-date and idiomatically correct, as each version is generally written by native speakers. You just go to the article in one language and then click through on the left-hand "in other languages" bar to get any number of translations. Then the full article even provides related vocabulary! When I'm looking for a translation but can't find the inter-language link, that's when I add it to the original article once I do find it.
