Chrome and Firefox can do this too and it's easy so I don't get the reliance on DuckDuckGo for it.
In Firefox you go to the wikipedia page, right click on the search text box, then "Add Keyword for this Search". In Chrome, you do the same thing, right click on that search box and then click "Add as Search Engine".
You can add whatever keyword you want, like "w" and from then on, all searches with "w " as a prefix will go straight to Wikipedia's results.
I have shortcuts defined for Wikipedia, Stackoverflow, Amazon.com, IMDB, a dictionary for my native language, my personal Gmail, my work Gmail, Google Translate and Hacker News.
For instance for Hacker News, I often want to search for articles I've read here, not to mention it's a valuable resource for getting other people's opinions on certain subjects. So instead of searching on Google for:
some topic site:news.ycombinator.com
I defined a prefix for this search "hn", and so I simply type "hn some topic". You can't use the shortcut for this though, you'll have to go to Settings and manually add a search engine setting.
For Google Translate, I basically type "enro phrase", for translating "phrase" from English to Romanian, while I type "roen phrase" for translating "phrase" from Romanian to English.