Magento 2.2.6 Language Switcher – Adding to Header.phtml File

The problem is a bug in the model Mage_Core_Model_Url_Rewrite_Request (Magento 1.8) and Mage_Core_Model_Url_Rewrite (earlier versions).

The section of core code in 1.8 looks like this:

    // Section from Mage_Core_Model_Url_Rewrite_Request::_rewriteDb()

    $fromStore = $this->_request->getQuery('___from_store');
    if (!$this->_rewrite->getId() && $fromStore) {
        $stores = $this->_app->getStores();
        if (!empty($stores[$fromStore])) {
            $store = $stores[$fromStore];
            $fromStoreId = $store->getId();
        } else {
            return false;
        }

The Bug: the value of the query parameter is the store code, (in my case de, en or fr). The keys of the array returned by app->getStores() are the numeric store IDs. Thats why if (!empty($stores[$fromStore])) { always fails.

Once that bug is fixed, another bug becomes apparent later in the same method (I think only in 1.8):

$targetUrl = $this->_request->getBaseUrl() . '/' . $this->_rewrite->getRequestPath();

The request objects base url always is the Magento base_url, without the store code. Using $currentStore->getBaseUrl() instead there fixes that bug, too.

Once those two issues are fixed the language switcher works fine. Here is an extension which does exactly that for Magento 1.8 (CE): https://github.com/Vinai/VinaiKopp_StoreUrlRewrites

In Magento 1.7 the issue might be something different. I still thought I'd add this answer, just in case google brings somebody else here who is running 1.8 or newer.

Tested, this and I can swap locales at will, and get the translations.

See Mage_Core_Model_Translate::getLocale()

which I changed to :

        /**
         * Retrieve locale
         *
         * @return string
         */
        public function getLocale()
        {
// custom code start to get current logged in customer            

if(Mage::getSingleton('customer/session')->isLoggedIn()) {
                $customerData = Mage::getSingleton('customer/session')->getCustomer();
                $this->_locale = 'en_US'; // here you would pull the locale from a customer attribute
            }

// custom code ends

            if (is_null($this->_locale)) {
                $this->_locale = Mage::app()->getLocale()->getLocaleCode();
            }
            return $this->_locale;
        }

Now when I view the frontend, the locale is loaded from the files in app/locale/en_US (as compared to my default locale of en_AU)

Naturally the above code shoudl be done via a rewrite. Don't go edit core files ;)

Hope this helps, or at least puts you on the right track.