MAGETWO-35032: Composite products can't be added to the order from 'Recently Viewed Products section' Fix original case

Author: vtymchynskyi

app/code/Magento/Quote/Model/Quote.php

@@ -1538,8 +1538,8 @@ public function addProduct(
         /**
          * Error message
          */
-        if (is_string($cartCandidates)) {
-            return $cartCandidates;
+        if (is_string($cartCandidates) || $cartCandidates instanceof \Magento\Framework\Phrase) {
+            return strval($cartCandidates);
         }
 
         /**