HTML5įirstly, HTML5 is the language most online slots are programmed in nowadays. This article will help you get your foot into slot machine programming, even as a beginner. Or you’re simply curious about what programming language slot machines are in.Įither way, we will list the best language for online games and explain how coding slots work. So, you want to learn how to code an online casino and are looking for the best language for games. we will list the best language for online games and explain how coding slots work. HTML5, Java, C++, JavaScript, C# are the 5 Best Languages for Developing Casino Games.