Here's a Keyboard Maestro macro that uses a rather primitive way to mask the info in DeepL-in.txt in segments that you send to DeepL:
I'll add the Python script to this posting.
Note that you'll need Keyboard Maestro 8 for this macro. I'll post an image of the macro with instructions for the fields to personalise, later.
Here's a MS Word document with a screenshot of the macro.
You'll need to change:
To the paths on your Mac.
I will try to rework this macro so that the tokens are generated on the fly (e.g. based on the position in the segment). Then it'll be possible to use a list with only one column, e.g. the list of non-translatables.