Fix signald not properly forwarding international characters

Signed-off-by: Magic_RB <magic_rb@redalder.org>

containers/mautrix-signal.nix

@@ -46,6 +46,7 @@ nglib.makeSystem {
                 SOCKET_PATH="/var/run/signald/signald.sock"
                 mkdir -p $(dirname $SOCKET_PATH)
 
+                export LANG=en_US.UTF-8
                 ${lib.getExe pkgs.signald} -d $DATA_DIR -s $SOCKET_PATH
               '';
       };