This thread isn't really useful unless you're really passionate about a language. Some programming languages in here may not be easy. If they do not compile directly into bytecode, you can't use them 100% in your mod and you still need to learn Java, lowering the usefulness of the "compatible" programming language. If they do compile directly into bytecode, they're going to involve compiling (when manual, running the compiler command everywhere) which might get tedious. Some of them have support for Gradle, making it easier when someone's worked on it. Spoiler: Scala Forge already adds support, you don't need to do much. I'd recommend the Eclipse Scala IDE plugin, really awesome. This one is an outdated but still somewhat valid tutorial. I recommend the Project Red Git repository or another overlooked mod called Project XY. Spoiler: Clojure/Lisp (by ljfa) @ljfa would be credited for this one. Here's a proof of concept project written in Clojure, which adds commands ingame for Clojure code. Clojure can compile into bytecode. Spoiler: Jython/Python You need to have the Jython standalone jar, and the user needs to have it in the mods folder (in which it would be injected into the classpath). Following this tutorial, you should be able to do a lot. Jython does not compile into bytecode, and its developers don't really update the project anymore, leading to further incompatibilities. I would recommend PyDev, but I don't really think there's any good Jython IDE. Still, use PyDev. Spoiler: JRuby/Ruby Pretty much like Jython, except JRuby has a compiler (how to use it) that compiles into bytecode. You can find tutorials on how to call Java from JRuby here. Even more information about JRuby can be found here. The JRuby jar needs to be in the classpath like the Jython jar too. @trajing has experimented with this before, and his work can be found here. I have taken some inspiration from him, since I don't know much about how JRuby works. I haven't tested it myself. Spoiler: Groovy This one is probably the easiest after Scala. It compiles directly into bytecode. I 100% recommend (and would kind of require) searching for "Groovy" on the Eclipse marketplace and installing the first result. It has a built-in compiler which gets rid of the manual compiling. Do note that this plugin needs Eclipse Mars instead of Eclipse Luna. Forge GradleStart works with it This has been tested and it does work. Proof and git repo I love Groovy at this point, and if you love it too, I'll create a GitHub repo to demonstrate how it works. Well, most Java code can basically be used as Groovy code, so I don't think you should have any problems. If you have any trouble or need help, feel free to ask. I won't ignore any questions.