If you port code over from one language to another, how can this be detected?
Say you were porting code from c++ to Java, how could you tell?
What would be the difference between a program designed and implemented in Java, and a near identical program ported over to Java?
If the porting is done properly (by people expert in both languages and ready to translate the source language's idioms into the best similar idioms of the target language), there's no way you can tell that any porting has taken place.
If the porting is done incompetently, you can sometimes recognize goofily-transliterated idioms... but that can be hard to distinguish from people writing a new program in a language they know little just goofily transliterating the idioms from the language they do know;-).