Drupal 6 to 8 migrations currently don't include translations of nodes.
Translated nodes in D6 use a tnid property that associates them into translation sets. There's also i18ncontent and i18ncck that take care of the nodes and fields.
- Add translation data to the drupal6 migration fixture.
- Update the content entity destination to support translations.
- Make the node migration sources include only the default translation.
- Add auxiliary migrations to bring in the translations.
Related issues will be handled as follow-ups:
- Make the auxiliary migrations auto-derived, so they don't need a template.
- Migrate translated node revisions.
- Migrate other entity types: users, terms, etc.
- Migrate related data: menu items, taxonomy term relations, node access rules, path aliases, visitor stats, etc.
- Handle references to translated nodes, ie: "node/5" might be a translation, will links to that still work?