A mod needs a language runtime that is not installed
Applies to Forge, NeoForge, Fabric, Quilt.
What it looks like in your log
Missing language provider: kotlinforforge
What causes it
A mod written in Kotlin or another JVM language needs its language runtime mod, and it is missing.
How to fix it
Install the language runtime mod the error names (Kotlin for Forge, or Fabric Language Kotlin).
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log