Localize user facing strings

[jtpio]

Fixes #49

Companion PR: jupyterlab/language-packs#903

[github-actions]

👈 Launch a Binder on branch jtpio/jupyter-chat/translator

[brichet]

Thanks a lot @jtpio for working on this, it looks great!

Some missing translation that we may want to handle (in chat model only):

• jupyter-chat/packages/jupyter-chat/src/model.ts

  Line 698 in c13de66

  message: `${unreadCount} incoming message(s) ${this._name ? 'in ' + this._name : ''}`

• jupyter-chat/packages/jupyter-chat/src/model.ts

  Line 705 in c13de66

  message: `${unreadCount} incoming message(s) in ${this._name}`

• jupyter-chat/packages/jupyterlab-chat/src/model.ts

  Lines 420 to 421 in c13de66

  	username: 'User undefined',
  	mention_name: 'User-undefined'

• jupyter-chat/packages/jupyterlab-chat/src/model.ts

  Lines 442 to 443 in c13de66

  	username: 'User undefined',
  	mention_name: 'User-undefined'

• jupyter-chat/packages/jupyterlab-chat/src/model.ts

  Lines 486 to 487 in c13de66

  	username: 'User undefined',
  	mention_name: 'User-undefined'

[brichet]

Thanks @jtpio.

We'll probably need to update jupyterlab/language-packs#903 with the translation domain.

[andrii-i]

Overall looks good. Please see one concern below worth noting and potentially addressing.

[andrii-i]

translator is omitted here so chat widgets opened via the file manager won't be translated - useTranslator() will fall back to nullTranslator for the entire component tree while side-panel mode correctly gets localization via MultiChatPanel. Worth extending ChatWidgetFactory.IOptions to accept and forward translator so document mode has full coverage too. Can be addressed in a follow-up PR.

[brichet]

This interface already extends DocumentRegistry.IWidgetFactoryOptions which includes a translator.
The property would be duplicated if not omitted, I think.

[jtpio]

Ah just realized this picked up a conflict. Just rebased to fix it.

[brichet]

Thanks @jtpio