TYPO3 Core

Fetching of the translated MM relation needs to be covered with functional tests.
We already have tests for FAL in
typo3/sysext/extbase/Tests/Functional/Persistence/TranslatedContentTest.php

We can extend the test covering existing relation to categories which is an MM relation configured as select (tree) field.
The categories field is configured in tt_content like:

        'categories' => 
        array (
          'exclude' => true,
          'label' => 'LLL:EXT:core/Resources/Private/Language/locallang_tca.xlf:sys_category.categories',
          'config' => 
          array (
            'type' => 'select',
            'renderType' => 'selectTree',
            'foreign_table' => 'sys_category',
            'foreign_table_where' => ' AND sys_category.sys_language_uid IN (-1, 0) ORDER BY sys_category.sorting ASC',
            'MM' => 'sys_category_record_mm',
            'MM_opposite_field' => 'items',
            'MM_match_fields' => 
            array (
              'tablenames' => 'tt_content',
              'fieldname' => 'categories',
            ),
            'size' => 20,
            'maxitems' => 9999,
            'treeConfig' => 
            array (
              'parentField' => 'parent',
              'appearance' => 
              array (
                'expandAll' => true,
                'showHeader' => true,
                'maxLevels' => 99,
              ),
            ),
          ),
        ),