How to select all similar objects above a "backgroud object" ?

I often receive PDFs that need to be translated into other languages. I need to delete the original text.
However, the PDFs provided by clients have already been converted to curves, and the densely packed text is all converted to curves, with each character as a separate object.

There’s just too much of it, the layers are a mess, and there are different backgrounds as well.
I’ve tried using the “Select Similar” tool, but it always selects completely unrelated text, so I’ve had no choice but to delete them one by one.

I’ve noticed a pattern: some characters are positioned on top of a specific object’s background.
Is it possible to use the background below as a selection boundary to select the text above it?
Is there a script or any clever workaround for this?

Thank you very much.

I’ve provided just a small sample; in reality, it’s much more complex than this.