Server Side language for iOS apps

I want to learn programming in Swift. But I don’t have a Mac right now. So I’m thinking of learning any server side language that could help me write the server side of my app. Can anyone please suggest a good server-side language? I’m thinking of opting for C# as it is also an Object-Oriented language but I can also go for PHP. Please suggest.

There are options available to learning swift when you do not have a Mac and are not prepared to spend money on purchasing one just yet.

Chris Ching has a YouTube video that describes how you can use an online virtual Mac (MacStadium) to create Apps.