Please confirm the deprecation date for Email setting API. And please provides the roadmap on this. As we will run into problems if we lose this support.
Bellow is the missing features -
Disclaimer: I work on Gmail and the Gmail API platform.
We're happy to announce that we have now released the new Gmail API delegate settings methods, effectively replacing the long since deprecated Email Settings API delegation settings methods.
You can now use the standard libraries and tools found at https://developers.google.com/gmail/api to interact with the new Gmail delegate settings methods.
We will be publishing a blog post at https://gsuite-developers.googleblog.com raising the visibility of the new delegate settings methods in the coming weeks, but I wanted to personally give you a courtesy heads-up.
Overview/introduction guide: https://developers.google.com/gmail/api/guides/delegate_settings
Reference documentation: https://developers.google.com/gmail/api/v1/reference/users/settings/delegates
Migration guide (from the deprecated Email Settings API delegation methods): https://developers.google.com/gmail/api/guides/migrate-from-email-settings#managing_delegation_settings
As for your concerns regarding the deprecated Email Settings API language settings and general settings methods, DaImTo's answer is correct:
These items are not currently available nor is there any information on when / if they will be.
UPDATE (April 25, 2019):
We have released Gmail API language settings methods, replacing the deprecated Email Settings API language settings feature!