Multilingual Form Validation

Trongate makes it easy to support form validation in multiple languages. The framework stores error messages in language-specific files and you can easily switch between languages on demand.

How It Works

Trongate's validation system loads error messages from language files based on the current language setting. When a validation error occurs, the framework displays the translated message for the selected language.

Language File Structure

Language files are stored in the following directory structure:

Each language uses a two-character ISO language code:

• en - English
• fr - French
• es - Spanish
• de - German
• it - Italian
• pt - Portuguese
• ja - Japanese
• zh - Chinese

Language File Format

Each language file contains a PHP array of error messages. Keys match the validation rule names, and values are the translated error messages:

Placeholder Substitution

Error messages use two types of placeholders that are automatically replaced. The framework supports both square-bracket and curly-brace formats:

Setting the Validation Language

Use set_language() to switch the validation language:

When validation fails, error messages will be displayed in French.

Resetting to Default Language

Use reset_language() to revert validation messages to the default language (English):

This method removes the language preference from the session, allowing the framework to use the default language.

Real-World Example: Multi-Language Site

Here's a complete example of a multilingual registration form:

In the view file, pass the language as a hidden field so it persists through form submission:

Adding a New Language

To add support for a new language, follow these steps:

Step 1: Create the Language Directory

Create a new directory in the validation module:

Step 2: Create the Language File

Create validation_errors.php in that directory with translated error messages:

Step 3: Use the New Language

Now you can use the new language in your validation:

Language Fallback Behavior

The validation system handles missing language files gracefully:

1. First, it looks for a language file matching the requested language code (e.g., fr/validation_errors.php)
2. If that file doesn't exist, it falls back to the default English language file (en/validation_errors.php)
3. If a specific error message key is missing from a language file, it displays a generic error message

Complete List of Language Strings

Here are all the validation error message keys you should include in your language files:

Standard Validation Rules

File Validation Rules

Image Validation Rules

Upload and Security Rules

Best Practices

1. Validate the language code: Always whitelist acceptable language codes before setting a language. This prevents invalid language codes from being used.
2. Pass language as a hidden field: When using forms, include the language as a hidden field so it persists through validation errors.
3. Use ISO 639-1 codes: Stick to two-character language codes (en, fr, es, etc.) for consistency and compatibility.
4. Keep language files in sync: When you add a new validation rule, update all language files with translations for that rule's error message.
5. Create a language constant (optional): Define the constant APP_LANG in your configuration (e.g., config/config.php) to set your application's default language. The Language module checks this constant if no session or cookie preference exists.
6. Store user language preference: Save the user's language preference in their account or a cookie for personalization.
7. Use natural field labels: Use lowercase, natural language for field labels so error messages read naturally in all languages: "email address" not "email_address".
8. Test all languages: Verify that error messages display correctly in each supported language before deploying.
9. Include comprehensive translations: Don't leave error messages in English if you're supporting other languages - translate all messages for a professional user experience.

Custom Error Messages in Different Languages

When using custom validation callbacks, define error messages in your language files and simply return the key - the framework will handle the rest.

For example, in a language file such as fr/validation_errors.php you could add:

Then, your validation callback could be written like so:

Configuration Constants

If you are building a website that does not have English as the default language, you can define a default application language in your configuration. The Language module (which validation uses) checks the constant APP_LANG:

The framework will use this default language if no language has been explicitly set via set_language() and no language preference exists in the session or cookies.

Session Behavior

The validation module integrates with Trongate's Language module. Language preference is stored in the session ($_SESSION['app_lang']) and optionally in a cookie:

• When you call set_language('fr'), it sets $_SESSION['app_lang'] = 'fr' and stores a cookie
• This preference persists across browser sessions (via cookie) and is shared with other application components
• When you call reset_language(), it removes the session variable and cookie
• When validating, the framework checks the Language module for the current language setting

Common Scenarios

Scenario 1: User Selects Language from Dropdown

Scenario 2: Load User's Preferred Language Automatically

Scenario 3: Multilingual API Response