One of the mods has an invalid animation json - but this mod is not mentioned
Start with GeckoLib and AzureLib and the mods requiring it
If this works, add the rest of your mods one by one or in groups until you find the one, causing this issue
Your new LanguageManager() is not the language manager that is being used when you call Minecraft.getInstant().getLocale().
Minecraft.getLanguageManager().setSelected(code); should work. Can you show that code?