If I understand you correctly, your filecontent is something like
<a href="myfile_e.shtml"> and you want it to be <a href="/french/myfile_f.shtml">
right? you need to include a way to match filenames. If, for example, you really are parsing links, you can use " as a marker. s!"([^"]+)_e\.shtml"!"/french/$1_f.shtml"!gs should work in that case.
If I didn't understand you correctly, please elaborate on exactly how your input looks like and what you want the output to be. Sorry for the long time it took to get an answer, it seems everyone missed your thread.
pretty much yes. And then vice-versa once they're in the English folder and they click on the link (.pl) it brings them to the French folder respectively. I'll give it a try and let you know if it will work switching from one language to the other. Thank you