What programming language should I learn to interface with Bitpay’s API?

 Bitpay’s API uses JavaScript Object Notation language (JSON) for communication with its API.  Because of this, Javascript is probably the most important language for any programmer to know when dealing with Bitpay’s API.  But Javascript cannot be used on its own.  You’ll also need to learn PHP and HTML to make use of it on a web page.  Bitpay has some great resources and samples for interfacing with its API in these languages.  Other non-web languages can be used with JSON, though it is less common to see.  Java, for example, can integrate JSON commands quite easily, but any common programming language, including C++, C#, .NET and Python, have community-created parsers and generators for JSON.  Ultimately, it matters less which language is best to use with Bitpay’s API, and more which language is appropriate for the sort of projects you’d like to create.