See my crash reports below. Note that the class ca.weblite.objc.NSObject is not found and relates to Java-Objective C bridge. No wonder why this bug only applies to Mac OS X which use Objective C as its native programming language. I verified it by running Minecraft 1.12 on Windows PC edition and it's all fine. The exception is thrown in the method com.mojang.text2speech.Narrator.getNarrator(Narrator.java:22) in which Narrator text to speech is introduced in Minecraft 1.12. This may have something to do with the library java-objc-bridge-1.0.0.jar which contains a .dylib Library and a META-INF directory.