Language shift for better performance

I have heard this many times that language X is faster than language Y. Sometimes the comparisions are done between languages of different generations but what worries me the most is when decision of language shift are taken for improving the performance. Being a Java programmer I have heard the debate of .Net faster than Java and the more old one being C++ faster than Java. All is fine until the language shift decisions are taken just because of performance reasons. It is like you have trie