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Cjammi - as you can see I have that option unchecked. Hopefully there is someone who does use that option - with multiple files open - who will be able to advise you best. I would have to experiment.
The word 'template' has a very specific meaning in calibre, it refers to things like this
{authors} - {title} which are used in tools such as Add Books, Save to Disk etc. I don't think you're referring to those templates. Perhaps you mean format files e.g. blah-blah.epub, blinky-bill.pdf etc.
I'm sure Kovid would welcome your expertise in improving the French edition of the User Manual, some info here ==>>
http://calibre-ebook.com/get-involved
BR