The #1188388: Entity translation UI in core issue was committed with a considerable number of follow-ups planned. The main reasons for this were reducing the initial patch size to something not too painful to review and ensuring we had an MVP in before feature freeze to be able to refine it afterwards.
This metaissue has the goal to track all the most important ET improvements: a new issue queue component has been created but we have some issues that don't belong to it.
Node translation replacement
#1498674: Refactor node properties to multilingual
#1952062: Remove legacy translation module in favor of content translation
#1834250: Hide Content Translation module until we are able to remove it
#1833184: Find a consistent naming scheme for translation-related modules
#1810386: Create workflow to setup multilingual for entity types, bundles and fields
#1977784: Content language settings configuration page needs to determine what entities and bundles to include
#1807366: Make fields translatable by default when enabling translation on a bundle
#1807776: Support both simple and editorial workflows for translating entities
#1832836: Discuss how to view original translation from translation form
#1498724: Introduce a #multilingual key (or similar) for form element
#1833022: Only display interface language detection options to customize more granularity
#1893568: Make each field instance have its own translatable property, instead of sharing translatable property with others.
#1833196: could not have interface in language A and create a translation from language B to language C
#1498880: Theme language switcher for seven theme
#1832870: Only show source translation column if there are > 2 source languages (more than n/a and the original language).
#1831608: Show or hide the "Make field translatable" checkbox on the add field form depending on translatability
#1833104: Add a "translatable" column to Manage Fields
#1914800: Dropbutton width is smaller than longest item
#1807902: add hint to field collapsed global settings: GLOBAL SETTINGS: Number of values (1), Field translation (disabled)
#1807908: Autofill revision log with text that describes action like: German translation added or Spanish translation edited
#1807830: Improve UI by adding hint to add translation: source language collapsed field set
API improvements and code clean-up
#1810370: Entity Translation API improvements
#1498720: Make the default SQL storage controller automatically generate tables for every defined entity type
#1807800: Add status and authoring information as generic entity translation metadata
#1446382: Need a reliable way to determine if a specific bundle for an entity type is translatable (Fixed in D8)
#1983928: translatable, translation enabled, multilingual, language-aware
#1916790: Convert translation metadata into regular entity fields
#1810394: Exploit hook_entity_prepare so not skipping access checks when adding translation
#1810350: EntityTranslationControllerInterface::get*Path() should not be translation specific
#1831530: Entity translation UI in core (part 2)
#1810320: Remove EntityTranslationControllerInterface::getAccess() once have entity access
#1810330: Move EntityTranslationControllerInterface::removeTranslation() into EntityInterface
#1498850: Rename the 'translatable' field property
#1848904: Bundles cannot be specified in Entity Translation tests
#1938384: "Undefined property" error only after adding translations to existing content.
#1968970: Remove translation_entity.module specific properties from the @EntityType annotation