The best language to get started in NLP is any language you like. Java, Ruby, Python, and C++ all have good libraries for natural language processing. Though some people here are partial to suggesting Python with NLTK, you can get an equally good NLP library in OpenNLP for Java or Stanford's JavaNLP, or LingPipe. And if C# is your forte, you can use SharpNLP.
One thing you don't need is a special purpose language or paradigm like Prolog or LISP. Prolog's logic paradigm with backtracking seems natural for thinking about context-free grammars, but in reality its backtracking method for parsing those grammars is slow compared to the Earley parser which can be implemented in imperative languages at least as well as it can be implemented in Prolog. It's also no easier to learn a grammar from text in Prolog. And LISP's ability to write self-modifying code won't particularly help you in NLP either.