With a good understanding of Java, JavaScript, and PHP, there is no need to learn C++ further before jumping into C#. If you already have the basic concepts down like casting variables, setting correct return types, etc. then you will be just fine learning C#. THe thing about .NET is that since it's a framework, it has so many speciallized functions and ways of doing things that are so different from the actual language's way of doing the same things, that it really won't be much benefit to you to learn both if you only plan on doing .NET. PHP and Java are already a whole lot like C/C++/C# that you won't need any special C++ knowledge to be able to pick it up quickly.
Also, don't bother learning Perl or Python, Perl isn't so widely used anymore, and Python has never really caught on to the mainstream. You're fine where you're at, and you will be much more prosperous developing for the .NET framework - just get on learning C#!