Please Follow Below steps to resolved such error of store switcher :

– Follow the below steps to resolve the switcher issue.

Step 1: You need to override the following file of the vendor module as mentioned below.

Override this File in your module :

vendor/magento/module-store/etc/di.xml

Step 2: Replace the following code :

 <type name="MagentoStoreModelStoreSwitcher"> 
     <arguments> 
         <argument name="storeSwitchers" xsi:type="array"> 
             <item name="cleanTargetUrl" xsi:type="object">MagentoStoreModelStoreSwitcherCleanTargetUrl</item> 
             <item name="manageStoreCookie" xsi:type="object">MagentoStoreModelStoreSwitcherManageStoreCookie</item> 
             <item name="managePrivateContent" xsi:type="object">MagentoStoreModelStoreSwitcherManagePrivateContent</item> 
             <item name="hashGenerator" xsi:type="object">MagentoStoreModelStoreSwitcherHashGenerator</item> 
         </argument> 
     </arguments> 
 </type>

with

 <type name="MagentoStoreModelStoreSwitcher"> 
     <arguments> 
         <argument name="storeSwitchers" xsi:type="array"> 
             <item name="cleanTargetUrl" xsi:type="object">MagentoStoreModelStoreSwitcherCleanTargetUrl</item> 
             <item name="manageStoreCookie" xsi:type="object">MagentoStoreModelStoreSwitcherManageStoreCookie</item> 
             <item name="managePrivateContent" xsi:type="object">MagentoStoreModelStoreSwitcherManagePrivateContent</item> 
         </argument> 
     </arguments> 
 </type>

Clean the cache and You are done.