"search update in a searchBox filter"

[mention:9322c334ce224857b6b7e2f011f055bd:e9ed411860ed4f2ba0265705b8793d05] 
You can't directly change the "search" text in Appian's record list search bar. It's built-in.

If you really want that then you can try this alternative approaches:-
1) You can create a custom interface using components like text fields and buttons. This allows you to customise the search button text to "chercher."
2) Add labels like "chercher" (Search by) near the search bar.

Wouldn't it be easier to have your user switch to french in the user settings?

docs.appian.com/.../Settings_Page.html