This might seem like a trivial question, but I'm researching solutions and couldn't seem to find which language this framework used. I know the frontend has to be HTML/CSS/Javascript, but what does it use on the backend?
What server side language(s) does Sitecore use?
Sitecore uses either ASP.NET Web Forms or ASP.NET MVC to generate the final HTML pages. This means developers can use any programming language of the .NET Framework. C# is one of the most popular with VB.NET but any other .NET Framework language like F# can be used.
That being said, most if not all Sitecore developers use C#.
While Sitecore itself is written in C#, that doesn't necessarily require a solution to be built in C#.
It is an ASP.NET-based product, so any language supported by ASP.NET will work. The most common of these are VB.NET and C#. C# is by far the most popular (and with good reason), however, you will find there are numerous languages that could be used if you really wanted to.
The key limitation is Visual Studio. Most .NET devs use Visual Studio and its designers and project systems are built around emitting and compiling C# and VB.NET only. If you're prepared to use other tools it should be completely plausible to code in C++ or Python.NET or F# or J# or COBOL.NET or ...
EDIT: this is an old post, and VS/VSCode have come a long way since, as such there are now numerous languages that can be used as 'first class citizens' in .NET - I believe there is even tooling for PHP these days if you're so inclined. C# is still the easy favourite FWIW.
