Language packs break JupyterLab on Python 3.7 completely

[krassowski]

Description

I just noticed while trying to test localization of an extension that language packs are broken with JupyterLab 3.1.13 and 3.1.12 (and possibly older too as the issue comes from jupyterlab_server/gettext) on binder, and they completely break JupyterLab UI once activated (by crashing server).

Reproduce

1. Install a language pack on binder or use a repro gist: https://gist.github.com/krassowski/b1737a6d77d29ea08dd7d73f39d159c1
2. Change language from Menu Settings → Language
3. See the page does not reload
4. See the error in console:

Traceback (most recent call last):
  File "/srv/conda/envs/notebook/lib/python3.7/site-packages/tornado/web.py", line 1702, in _execute
    result = method(*self.path_args, **self.path_kwargs)
  File "/srv/conda/envs/notebook/lib/python3.7/site-packages/tornado/web.py", line 3173, in wrapper
    return method(self, *args, **kwargs)
  File "/srv/conda/envs/notebook/lib/python3.7/site-packages/jupyterlab_server/settings_handler.py", line 54, in get
    translator=translator.translate_schema
  File "/srv/conda/envs/notebook/lib/python3.7/site-packages/jupyterlab_server/settings_utils.py", line 342, in get_settings
    schema = translator(schema)
  File "/srv/conda/envs/notebook/lib/python3.7/site-packages/jupyterlab_server/translation_utils.py", line 737, in translate_schema
    translator._translate_schema_strings(translations, schema.copy())
  File "/srv/conda/envs/notebook/lib/python3.7/site-packages/jupyterlab_server/translation_utils.py", line 696, in _translate_schema_strings
    schema[key] = translations.pgettext(context, value)
  File "/srv/conda/envs/notebook/lib/python3.7/site-packages/jupyterlab_server/translation_utils.py", line 490, in pgettext
    return gettext.dpgettext(self._domain, msgctxt, msgid)
AttributeError: module 'gettext' has no attribute 'dpgettext'

5. Reload manually
6. See JupyterLab not loading due to server errors

Expected behavior

Language packs work, UI server does not crash

Context

• Operating System and version: Linux Ubuntu 21.04
• Browser and version: Chrome 92
• JupyterLab version: 3.1.13

[krassowski]

It seems that this Binder is currently picking Python 3.7.10. The context translations functions are only available in Python 3.8. I think that we did not use context translations prior to jupyterlab_server 2.8.0 (released 18 days ago) which included translation of settings schema (jupyterlab/jupyterlab_server#205 by @fcollonval).

It looks like other projects were bitten by this too: napari/napari#2299 and @goanpeca has had prepared a workaround there: napari/napari#2305. Should we just fallback to non-context alternatives too?

[krassowski]

Also, I think that we should add integration testing across jupyterlab-language-packs, jupytelab-server and jupyterlab so that it does not happen again.

[goanpeca]

It looks like other projects were bitten by this too: napari/napari#2299 and @goanpeca has had prepared a workaround there: napari/napari#2305. Should we just fallback to non-context alternatives too?

Sure, we can do that, will open a PR!

[krassowski]

Already opened one: jupyterlab/jupyterlab_server#213