AddSliceContainer.jsx can't be translated by messages.json

A clear and concise description of what the bug is.

Expected results

AddSliceContainer.jsx can be translated

Actual results

All other pages can be translated correctly, except AddSliceContainer.jsx cannot.

Screenshots

No.

How to reproduce the bug

I run a development flask and dev-server in my computer to test translation. I found that AddSliceContainer.jsx can not be translated well, meanwhile other pages can be translated correctly.

Environment

• superset version: 0.35 and 0.34
• python version: 3.7
• node.js version: v10.16.0
• npm version: 6.9.0

Checklist

Make sure these boxes are checked before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if there are any.
• I have reproduced the issue with at least the latest released version of superset.
• I have checked the issue tracker for the same issue and I haven’t found one similar.

Additional context

No.

[cdmikechen]

Finally found the cause of the problem~

1. In superset/assets/src/preamble.js superset must get document id app to set @superset-ui/translation config. But AddSliceContainer.jsx replace id app to js-add-slice-container.
2. In superset/views/core.py web response must contain bootstrap_data.common node, so that superset/assets/src/preamble.js can read translation messages.

"common": self.common_bootstrap_payload(),

But /chart/add response data doesn’t have this node.

        return self.render_template(
            "superset/add_slice.html",
            bootstrap_data=json.dumps(
                {"datasources": sorted(datasources, key=lambda d: d["label"])
            ),
        )

We need to add this element like this:

        messages = get_flashed_messages(with_categories=True)
        locale = str(get_locale())
        common_bootstrap = {
            "flash_messages": messages,
            "conf": {k: conf.get(k) for k in FRONTEND_CONF_KEYS},
            "locale": locale,
            "language_pack": get_language_pack(locale),
            "feature_flags": get_feature_flags(),
        }

        return self.render_template(
            "superset/add_slice.html",
            bootstrap_data=json.dumps(
                {"datasources": sorted(datasources, key=lambda d: d["label"]),
                 "common": common_bootstrap}
            ),
        )

If I can, I think I will take some time to fix this problem by a PR recently

[chengkaisheng]

It helps. Thanks!