config: mark an error message up for translation

Signed-off-by: NChristian Couder <chriscool@tuxfamily.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

config.c

@@ -1701,8 +1701,8 @@ int git_config_get_untracked_cache(void)
 		if (!strcasecmp(v, "keep"))
 			return -1;
 
-		error("unknown core.untrackedCache value '%s'; "
-		      "using 'keep' default value", v);
+		error(_("unknown core.untrackedCache value '%s'; "
+			"using 'keep' default value"), v);
 		return -1;
 	}