prefer the venv pybabel but allow the system one to be used (if found)

compile-messages.sh

@@ -1,11 +1,13 @@
 #!/bin/sh
 . ./etc/translation.vars
 
+export TZ=UTC
+
 if [ $# -ge 1 ]
 then
-    TZ=UTC env/bin/pybabel compile -D $1 -d $TRANSDIR
+    $PYBABEL compile -D $1 -d $TRANSDIR
 else
     for domain in $(ls $BABELCFG); do
-        TZ=UTC env/bin/pybabel compile -D $domain -d $TRANSDIR
+        $PYBABEL compile -D $domain -d $TRANSDIR
     done
 fi