Migrate Drupal 7 core node translations to Drupal 8

Problem/Motivation

Migrate D7 multilingual nodes.

Original report by Ryan Weal

Language setting (D6/D7 language field -> D8 language field). This will bring the language of the piece of content (EN/FR etc.) could also be LANGUAGE_NONE/UND/"language neutral" if it is either not translatable OR if it is the fallback in the case that one of the languages does not have a translation.

Translation node ID (D6/D7 tnid column -> D8 setting?). Associates a piece of content that is not set to UND/neutral

Title (D7 contrib "title" -> D8 title-contrib or core title if has been converted to translatable entity). This module is used in cases where entity translation is used and it was necessary to "override" the title field on nodes and taxonomies where multiple versions of this field are necessary. The title module migrates existing titles into a field, so if this module is enabled on a content type this field should be considered authoritative and override the default "title" field of the node.

Content translation vs. Entity translation structure:

.
├── content_translation
│   ├── nid_1
│   │   ├── field_body
│   │   │   └── language_none
│   │   ├── field_multi
│   │   │   └── language_none
│   │   ├── field_title
│   │   │   └── language_none
│   │   ├── language_en
│   │   └── tnid_2
│   └── nid_2
│       ├── field_body
│       │   └── language_none
│       ├── field_multi
│       │   └── language_none
│       ├── field_title
│       │   └── language_none
│       ├── language_fr
│       └── tnid_1
└── entity_translation
    └── nid_1
        ├── field_body
        │   ├── language_en
        │   └── language_fr
        ├── field_multi
        │   └── language_none
        ├── field_title
        │   ├── language_en
        │   └── language_fr
        └── language_none