If the argument starts with \", we are out of luck (at least I have not found yet a way how to encode the string '\\"foo' properly for my batchfile

Using the following cmd file as the mechanism of demonstration (called echoem.cmd):

@echo off

perl -wle"print qq['$_'] for @ARGV" %*
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Does this achieve what you are after?

C:\test>echoem "\"foo" "bar \"qux" \\\"foo
'"foo'            ### $1
'bar "qux'        ### $2
'\"foo'           ### $3
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