Header Editor Automatically Sets Language of All Tracks to English
When opening a file in the header editor, it automatically sets the language for all tracks to English.
So even if you do nothing and try to close the file, it will warn that the file was modified.
For files containing multiple tracks, it means you need to manually set them to what they were.
Here is the file loaded in the multiplexer and the same untouched file in the header editor: