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Not quite all public domain. (in English)  (maybe? gray area)
I'd highly recommend checking out his work on (and coining of the term) "language games"  I'm not sure I agree with all of the thinking behind them, but it's a fascinating concept that has useful nuggets whether or not you agree with everything Wittgenstein says about them. They are explored pretty fully in his work "Philosophical Investigations"  This work pretty much set aside a fair amount of his thinking in Tractatus Logico-Philosophicus, which is still an interesting work in its own right. I think that even a cursory ELI5 treatment of this material in a standard college course would be very useful in arming students with tools needed to dissect language. I've used it (in brief) when teaching a course on Informal Logic in relation to propaganda.
 It seems copyright on the English translation might still be in effect, or at least a gray area of determination. Since it's a common text use in college courses I'm guessing the copyright owners may fight public domain release. The issue will be whether or not the translation was a work for hire or if it can be considered sufficiently different to constitute an original work. The English translation by Anscombe, Hacker, and Schulte occured posthumously, and so might not be considered work for hire. Hopefully it will resolve in favor of public domain. For a shorter consideration of "language games" check out Blue Book.