I try to rewrite Sphinx-4 in C# ,
So Am I violating licence or anything like that
The Grand Janitor
Very interesting. I love to Sphinx be ported to different languages.
Sphinx has a very liberal license so I don't think you will violate any terms.
Of course, keep us up to date of where you are. If Sphinx has a C# branch, it will attract another group of enthusiasts.