I use replace(/[^\\w\\s]|_/g, \"\").replace(/\\s+/g, \" \") can filter all special character, but I don\'t want filter the French letters.
replace(/[^\\w\\s]|_/g, \"\").replace(/\\s+/g, \" \")
You can use this:
/[^\w\sàâäôéèëêïîçùûüÿæœÀÂÄÔÉÈËÊÏΟÇÙÛÜÆŒ]/g
You don't need special treatment for the _ as it is included in \w
_
\w
Reference
French orthography