Yii2下拉框切换语言问题：仅生效一次，刷新后恢复英文

Hey there! Let's break down why your language dropdown only works once and resets to English after a refresh. The root problem is that you're not persisting the user's language selection—right now, you send the choice to the server, but there's no code to save that preference (like in a session or cookie), so the app defaults back to English every time the page reloads.

Here's how to fix it step by step:

1. Update the View to Reflect Saved Language #

First, make sure the dropdown loads with the user's saved language pre-selected instead of always defaulting to English. Modify your select element like this:

<select class="form-control user_language">
    <option value="en" <?= Yii::$app->language === 'en' ? 'selected' : '' ?>>English</option>
    <option value="nl" <?= Yii::$app->language === 'nl' ? 'selected' : '' ?>>Norwegian</option>
</select>

This checks the current application language (which we'll set based on saved preferences) and marks the correct option as selected.

2. Enhance the JavaScript to Handle Initialization & AJAX #

Update your JS to initialize the dropdown on page load and ensure the AJAX request properly communicates with the backend to save the language:

<script>
$(document).ready(function() {
    // Set dropdown to saved language when page loads
    const savedLanguage = '<?= Yii::$app->language ?>';
    $('.user_language').val(savedLanguage);

    // Handle language change event
    $(".user_language").change(function(){
        const selectedLang = this.value;
        $.ajax({
            url: '<?= Yii::$app->request->baseUrl . '/site/set-language' ?>', // Replace with your actual controller route
            method: 'POST',
            data: { language: selectedLang },
            success: function() {
                // Reload the page to apply the new language immediately
                window.location.reload();
            },
            error: function() {
                alert('Oops, something went wrong while changing the language.');
            }
        });
    });
});
</script>

3. Add Backend Logic to Save Language Preference #

You need a controller action to receive the language choice, validate it, and save it (we'll use both session and cookie for persistence). Add this to your SiteController (or relevant controller):

public function actionSetLanguage()
{
    if (Yii::$app->request->isPost) {
        $language = Yii::$app->request->post('language');
        
        // Only allow supported languages to prevent invalid inputs
        $allowedLanguages = ['en', 'nl'];
        if (in_array($language, $allowedLanguages)) {
            // Save to session for temporary persistence (until user closes browser)
            Yii::$app->session->set('language', $language);
            
            // Optional: Save to cookie for long-term persistence (30 days)
            $languageCookie = new \yii\web\Cookie([
                'name' => 'user_language',
                'value' => $language,
                'expire' => time() + (3600 * 24 * 30), // 30 days from now
                'httpOnly' => true,
            ]);
            Yii::$app->response->cookies->add($languageCookie);
            
            // Update the app's current language immediately
            Yii::$app->language = $language;
        }
        
        return $this->asJson(['success' => true]);
    }
    
    return $this->asJson(['success' => false]);
}

4. Load Saved Language on App Bootstrap #

To make sure the app uses the saved language on every request, update your config/web.php (or relevant config file) to check for the session/cookie and set the language early:

return [
    // ... other configs
    'language' => function() {
        // Check session first, then cookie, default to 'en'
        if (Yii::$app->session->has('language')) {
            return Yii::$app->session->get('language');
        } elseif (Yii::$app->request->cookies->has('user_language')) {
            return Yii::$app->request->cookies->getValue('user_language');
        }
        return 'en';
    },
    // ...
];

Why This Works: #

• Persistence: We save the language choice in both session (temporary) and cookie (long-term) so it stays even after page refreshes or browser restarts.
• Initialization: The dropdown loads with the saved language instead of always defaulting to English.
• Validation: We only allow supported languages to avoid invalid inputs.
• Immediate Application: Reloading the page after AJAX success ensures all content updates to the selected language right away.

内容的提问来源于stack exchange，提问作者Yasin Patel