Update addons/frag/stringtable.xml

The translation is fine, it just didn't make it into the save file.
On my computer, however, it's fine.

Co-authored-by: johnb432 <58661205+johnb432@users.noreply.github.com>

addons/frag/stringtable.xml

@@ -156,7 +156,7 @@
             <Russian>Включает визуальную трассировку фрагментации и осколочных снарядов.</Russian>
             <Italian>Abilita il tracciamento visivo di effetti di frammentazione e spalling.</Italian>
             <Spanish>Habilitar trazado visual de los proyectiles generados por la fragmentación y el astillamiento.</Spanish>
-            <French></French>
+            <French>Active le suivi des éclats/explosions.</French>
         </Key>
         <Key ID="STR_ACE_Frag_HitSphereEnable">
             <English>Draw Event Spheres</English>