I should also note that all the inserted binary data is 0x80 or higher. I don't want to just clear the 0x80 bit, that results in junk in my text. I want to delete all characters 0x80 or higher. I'm ...

Before we get started with the steps, first try and reinstall Minecraft to ensure there are no corrupt files causing issues. Make sure you save your worlds properly so you don't lose any progress.