Views list of terms results in duplicate records because JOIN does not include langcode

I wonder if the issue is in EntityViewsData? It might be a generic issue with all entities, not just terms.

The code in EntityViewsData::getViewsData() should look like this:

    if ($data_table) {
      $data[$base_table]['table']['join'][$data_table] = [
        [
          'left_field' => $entity_id_key,
          'field' => $entity_id_key,
          'type' => 'INNER',
        ],
        [
          'left_field' => 'langcode',
          'field' => 'langcode',
          'type' => 'INNER',
        ],
      ];

Unfortunately that doesn't work.

This seems to cover it:

    if ($data_table) {
      $data[$base_table]['table']['join'][$data_table] = [
        'left_field' => $entity_id_key,
        'field' => $entity_id_key,
        'type' => 'INNER',
      ];
      // If the entity type is translatable another JOIN condition is required
      // on the langocde column to avoid duplicate records.
      if ($this->entityType->isTranslatable()) {
        $data[$base_table]['table']['join'][$data_table]['extra'][] = [
          'field' => $entity_keys['langcode'],
          'left_field' => $entity_keys['langcode'],
        ];
      }

A patch containing the code from #4.

This is related to 🐛 Views entity reference relationships must join on langcode for translatable entities Needs review but that only covers entity_relationship fields, not this core issue.

This needs to be turned into a merge request and needs test coverage.

Surely, this is 11.x?

I logged it against 10.3.x while I was first diagnosing the problem.