I can't replicate the problem. When I run the program with the two sentences:

$_= "This is a perl script/program-  code.";
my $target= "C'est un perl script / programme  -  codele";
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I get as the result in $target:

C'est un perl script/programme-  codele
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... which is what I expect. If you tell us the exact input data and the exact output data you get, maybe we can work on finding the cause.