On the whole, I'd have to say: No. This site is supposed to be about reviewing the code, posting a working version of the code in another language doesn't always help the OP. If you are suggesting an alternative algorithm, or you want to illustrate a point, using a language you are more comfortable with is fine, but answering a review request by posting the same program, written in another language just doesn't sit well with me.
Just allowing different language answers would, perhaps, put us at risk of becoming a half-arsed codegolfing site (which already exists). It'd also devoid what little meaning the tag-score has. Someone with a bronze, or silver badge in C should have proven he knows his way around C. If we were to allow answering in other languages, he might've answered everything in Java, and know very little about actual C, and memory management and all of the low-level stuff.
So in resuming: On the whole, an answer can contain snippets in an array of languages, provided the answer itself reviews the code the OP written. The remarks and suggestions must bare relevance to the OP's language of choice.
Demonstrating concepts/algorithms can be done in most any language, but I do think it's quite obvious that you can't truly review C code using Scheme. The languages are just too far apart.
When in doubt: post pseudo code
cf comments below: I'm not familiar with C#, but the syntax makes it (up to a point) acceptable to post Java and or C++ based answers. But if you're not sure how something is expressed in C#, if it can be expressed at all, just write pseudo code, not VB, Haskell or Lisp.