This is a server side only mod to provide i18n for server side only mods.
Language detection is automatically so players don't need to do anything.
This mod is not needed on client
You need to put language jsons in data/<mod id>/lang/, in vanilla assets pack format.
The only API is ServerI18n class.
Examples:
Text.literal(ServerI18n.translate(player,"translation key","arg1","arg2"))
ServerI18n.broadcast(server,"translation key","arg1","arg2")