Log:
latest.log

Steps to reproduce:

• Set language to turkish either through pc settings or jvm flag -Duser.language=tr
• Try to start the game with MAVM

Likely Solution:
Specify the Locale that is used when converting the name of the variant to lowercase here

variant.name().toString.toLowerCase(Locale.ROOT)

Java uses, by default, the locale of the pc/jvm args for the conversion. This can lead to issues like this when using languages like turkish (and others) where lowercase "i" actually is "ı".
Locale.ROOT is neutral and will correctly convert the string.

Alright, going to apply this patch.