How to unload language sources?

I am using language sources with asset bundles, and load them only in the scenes when I need them.
But I noticed these language sources will automatically move themselves under DontDestroyOnLoad thus never being unloaded.
I was expecting that local resources will be destroyed and release the resources.
Since there's a rather huge amount of text in my game, I wish to dynamically load and unlaod language sources and terms.
Is there a way to do so?