$string =~ s|\=\=\s+?([a-z0-9_ &\[\]ÀÂÄàâäÇçÉÊÈËéêèëÏÌÎïìîÖÔÒöôòÜÛÙüûù
+A-Z?!;«»()"]+)\s+?\=\=|==$1==|ge;
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In your input data there is no string that has both, whitespace at the start and at the end. Maybe you want \s* instead of \s+? ? Note that appending a ? modifier is likely useless your case anyway, as you want to remove all whitespace before/after the ==, so it doesn't make sense to make that removal non-greedy.