What It Does
Fabric Language Kotlin is a libraries and APIs project for the Fabric loader that makes it possible to write mod code in Kotlin. It adds no gameplay content on its own. Other mods written in Kotlin declare it as a dependency so their code can load correctly. It provides a Kotlin adapter for Fabric's entrypoint system, so a mod's fabric.mod.json file can set the adapter property to kotlin and point at Kotlin code. The repository documents entrypoint samples for class references, object references, companion object references, and top level function references.
Because it only needs Fabric Loader to be present, it doesn't rely on a specific Minecraft version to function. Whatever version your Fabric setup targets, the matching build of this library is meant to run beside it.
Who It's For
Players don't usually install this for a feature of its own. Real talk, it's aimed at people who write Kotlin based Fabric mods and at anyone running a mod that requires it. If a mod you download lists Fabric Language Kotlin as required, this is the piece that lets that mod's Kotlin code run. Mod authors use it as their entrypoint adapter and as a shared source of Kotlin libraries instead of packaging their own copies.
What It Bundles
From the org.jetbrains.kotlin namespace, the project bundles the Kotlin standard library and the Kotlin reflection library. From the org.jetbrains.kotlinx namespace, it bundles kotlinx-coroutines-core and kotlinx-coroutines-jdk8 for coroutines; kotlinx-serialization-core, kotlinx-serialization-json, and kotlinx-serialization-cbor for serialization; and atomicfu, kotlinx-datetime, kotlinx-io-core, and kotlinx-io-bytestring. Dependent Kotlin mods can rely on these shared copies rather than shipping their own.
Compatibility
Fabric Language Kotlin supports the Fabric loader. On Modrinth the client side is listed as optional and the server side is listed as optional, so it can fit a client only, server only, or combined install depending on what the mods that depend on it require. It's released under the Apache License 2.0. Its Modrinth category is Libraries & APIs and its author is modmuss50. The project lists support for dozens of individual Minecraft versions, including releases in the 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, and 1.21 families along with several newer numbered releases, so the exact build you need depends on the specific version your Fabric Loader install targets.
