do not override config when intl is not installed

fixes #5260

framework/CHANGELOG.md

@@ -4,6 +4,7 @@ Yii Framework 2 Change Log
 2.0.0 under development
 -----------------------
 
+- Bug #5260: `yii\i18n\Formatter::decimalSeparator` and `yii\i18n\Formatter::thousandSeparator` where not configurable when intl is not installed (execut, cebe)
 - Bug: Date and time formatting now assumes UTC as the timezone for input dates unless a timezone is explicitly given (cebe)
 - Enh #4275: Added `removeChildren()` to `yii\rbac\ManagerInterface` and implementations (samdark)
 

framework/i18n/Formatter.php

@@ -208,10 +208,14 @@ class Formatter extends Component
         }
         $this->_intlLoaded = extension_loaded('intl');
         if (!$this->_intlLoaded) {
+            if ($this->decimalSeparator === null) {
                 $this->decimalSeparator = '.';
+            }
+            if ($this->thousandSeparator === null) {
                 $this->thousandSeparator = ',';
             }
         }
+    }
 
     /**
      * Formats the value based on the given format type.