Language Preference: Implementing Translations in FEM

[goplayoutside3]

Currently PFE implementation of language preference does not persist between sessions. There's at least one issue open because volunteers would prefer to keep their language preference when the browser is refreshed (Example project: Every Name Counts Issue #5729).

While building language translations for FEM, we have the opportunity to implement persistent language preference between sessions. I'm opening an issue here for discussion of two questions:

1. Should the language preference be loaded from panoptes via request, or loaded from a cookie?
2. If language preference is fetched from panoptes, will it be stored on the User resource, or some other location?

[camallen]

The User model has an array attribute to store the preferred languages strings of an individual volunteer,

panoptes/db/structure.sql

Line 1777 in 2794e5b

languages character varying[] DEFAULT '{}'::character varying[] NOT NULL,

https://panoptes.docs.apiary.io/#reference/user/user

This setting is used as a persisted API side setting to ensure the user is presented with content in their desired language,

panoptes/app/controllers/api/api_controller.rb

Line 86 in 2794e5b

api_user.try(:languages) || []

You can use this attribute to provide a list of preferred languages, e.g. 'es, it, he, en-gb' which can be used to select any known translations that match these preferences (prioritized set intersection) to wire up the UI. See our translations system for local codes https://github.com/zooniverse/pandora/blob/2030aa5992b5586181d0b72b1a80680f7310765f/src/constants/languages.js