For what language editions of Wikipedia do no traditional encyclopedia counterparts exist?

Interesting question! It seems that a good way to answer it would be to perform a cross-checking of the "List of encyclopedias by language" [1] with "List of Wikipedias" [2], [3]. The format of those lists is not easily parsable/comparable, though, so I'll leave these links as pointers for someone wiling to do the analysis.

EDIT: Couldn't resist it. I performed a rudimentary parsing in [1] and [2] and used AWB's excellent list comparer tool to match the two sets of languages. It turns out that out of the 260 wikipedia editions, 220 don't seem to have physical counterparts (at least they're not listed in [1]). I'll put the list in [4], for convenience.

An interesting detail: there's one <s>physical</s> encyclopedia that doesn't have a Wikipedia counterpart: Leonese [5], which shares the language code as Asturianu (ast) -- for which there is indeed a Wikipedia, btw.

EDIT 2: My bad: the Leonese encyclopedia is afterall not a traditional one, but a wiki instead. Fixed above.

If I was a contestant on Jeopardy, I'd say Nahuatl. Though it's possible that those Native Americans had their own kind of encyclopedia thousands of years prior to the Europeans. With more time to think about it, I'd investigate the many variants of European languages that are tied to one small geographical region. With Alemannisch, for example, its speakers have probably have had to make do with Brockhaus. I don't know if the Slovenians have their own encyclopedia in Slovene. With two million speakers and their own country, I'd make that my Final Answer.

Simple English Wikipedia -- because nobody would be dumb enough to publish on paper an encyclopedia edition THAT stupid.