i18n(fr): fix untranslated UI strings, extract hardcoded ones, complete French catalog (#14164)

src/slic3r/Utils/Repetier.cpp

@@ -90,7 +90,7 @@ bool Repetier::test(wxString &msg) const
             }
             catch (const std::exception &) {
                 res = false;
-                msg = "Could not parse server response";
+                msg = _L("Could not parse server response.");
             }
         })
         .perform_sync();