Node red internationalisation does not work

Hi,
I am trying internationalisation following Internationalisation : Node-RED (nodered.org), here is how I did,

step 1:
in /app/nod_red/lower_case/locales/en-US, added lower-case.json, with content:

{
        "lower-case" : {
                "help-text" : "A simple node that converts the message payloads into all lower-case character"
        }
}

and /app/nod_red/lower_case is the node directory.

step 2
in lower-cas.js which in /app/nod_red/lower_case, added code

 node.log(RED._("lower-case.help-text"));

it showed the help text correctly.

step 3
in lower-cas.html which in /app/nod_red/lower_case, changed help node to

<script type="text/html" data-help-name="lower-case">
    <p data-i18n="lower-case.help-text"></p>
</script>

restarted node red, refreshed browser, and found the help text was not shown in browser.
17047700098941

Could someone help?