It depends on what you are trying to achieve. A lot of things in BizTalk can be done without c# or other .Net code, but then you will encounter some things that might require some code, and c# is one of the options.
For example scripting factoids in maps can use
- C# .NET
- JScript .NET
- Visual Basic .NET
For custom pipeline components again it just has to be .Net, not necessarily c#
I've even used a custom adapter in BizTalk that is written in Java.
For Azure, if you are using Logic Apps, again you might not need to do any coding at all. But again, you might hit scenarios where it makes sense to use Function Apps, again the code can be in multiple languages
Azure for developers overview
Azure supports the most popular programming languages in use today, including Python, JavaScript, Java, .NET and Go.