diff -u b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TaxonomyVocabularyTranslation.php b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TaxonomyVocabularyTranslation.php
--- b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TaxonomyVocabularyTranslation.php
+++ b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TaxonomyVocabularyTranslation.php
@@ -38,9 +38,11 @@
       ->fields('lt', ['lid', 'translation'])
       ->condition('i18n.type', 'vocabulary');
     $query->addField('lt', 'language', 'language');
-    // The vid is an integer and the objectid is a string. Use the like operator
-    // to force PostgreSQL to cast the vid to a string.
-    $query->join('i18n_strings', 'i18n', 'v.vid like i18n.objectid');
+    // The i18n_strings table has two columns containing the object ID, objectid
+    // and objectindex. The objectid column is a text field. Therefore, for the
+    // join to work in PostgreSQL, use the objectindex field as this is numeric
+    // like the vid field.
+    $query->join('i18n_strings', 'i18n', 'v.vid = i18n.objectindex');
     $query->leftJoin('locales_target', 'lt', 'lt.lid = i18n.lid');
 
     return $query;