Superset i18n: Save user's chosen language to user settings

[pomegranited]

Description

When changing the language settings in Superset, the changes are not saved upon closing and reopening the application. For example, if the default language is English and I change it to Spanish, Superset reverts back to English after restarting. Additionally, if I open Superset in a different browser after setting it to Spanish, it also defaults back to English. This becomes problematic when multiple users are involved. If User 1 prefers Spanish and User 2 prefers English, only one default language can be set, requiring one user to change the language every time they log in. The expected behavior is that once a user changes the language setting, it should persist across sessions.

Supporting Information

• Part 2 of Issues with Language Settings in Superset: Configuration Not Saved, Partial Translations, and Redirects apache/superset#30334

Proposed solution

• Add a new field to the user's Personal Information table which stores the user's preferred language, visible from User Info (/users/userinfo/):
  
• Use this setting (or to Superset's default language if no language preference is configured) to set the current language when the user logs in
• Users can update this setting using the same language dropdown UI element already in Superset.

[bmtcril]

Just noting that this is an upstream Superset enhancement, but is an improvement we want for Aspects.