set env in subprocess a little more cleanly

clients/urwid/main.py

@@ -1601,7 +1601,9 @@ class App(object):
         descriptor, path = tempfile.mkstemp()
         with open(path, "w") as _:
             _.write(init_body)
-        call("export LANG=en_US.UTF-8; %s %s" % (self.prefs["editor"], path), shell=True)
+        env = os.environ.copy()
+        env['LANG'] = 'en_US.UTF-8'
+        call("%s %s" % (self.prefs["editor"], path), env=env, shell=True)
         with open(path) as _:
             body = _.read()
         os.remove(path)