Troubleshooting Common PHP Warnings and Errors in Polylang

Many WordPress users rely on the Polylang plugin to create multilingual websites. However, like any complex software, it can sometimes interact unexpectedly with other themes, plugins, or server configurations, leading to PHP warnings and errors. This guide will help you diagnose and resolve some of the most common issues based on community reports.

Common Polylang Error Scenarios and Their Fixes

1. XML Parser Warnings from wpml-config.php

The Problem: You may see warnings about a "tag mismatch" in a file named wpml-config.xml, pointing to a Polylang file. This is not a bug in Polylang itself.

Why It Happens: Polylang can read a wpml-config.xml file from your theme or another plugin for compatibility. The warning indicates this file contains malformed XML, which Polylang cannot parse correctly.

The Solution: The issue is in the theme or plugin providing the faulty XML file (e.g., the 'capeone' theme in one example). You must locate and fix the XML error in that file. Contact the theme/plugin author for support or temporarily rename the file if you cannot fix it.

2. "Invalid argument supplied for foreach()" Warnings

The Problem: Warnings appear mentioning language-factory.php on line 161 or similar, often after changing a site's URL.

Why It Happens: This typically occurs when Polylang's internal language data becomes corrupted or is in an unexpected state.

The Solution: Navigate to Languages > Settings > URL Modifications in your WordPress admin and simply click "Save Changes" without altering any settings. This often triggers a routine that repairs the data. If the problem persists, it could be caused by phantom language entries in the database; a more advanced database cleanup may be required.

3. Warnings About Array Access on Null or Boolean Values

The Problem: Errors like "Trying to access array offset on value of type null" or "Attempt to read property 'slug' on bool" appear in logs or on the front end.

Why It Happens: These are often strict PHP 8+ warnings that reveal a function is trying to use a variable that is not an array or object as if it were. This can be caused by a misconfigured language parameter in a URL (e.g., lang=uk%2F instead of lang=uk) or by a third-party filter hook returning an unexpected value.

The Solution:

• Check URLs: Ensure all language switcher links and manually created URLs use the correct language code format without extra characters.
• Identify Conflicting Code: As seen in Thread 12, a filter like pll_rel_hreflang_attributes might be returning a null value instead of an array. Disable other plugins and switch to a default theme to identify the culprit, then ensure the custom code using Polylang's filters returns the correct data type.

4. Language Redirect Issues on the Homepage

The Problem: The main page (e.g., https://example.com/en) incorrectly redirects to the default language, while other pages work fine.

Why It Happens: This is frequently a server configuration issue, often related to .htaccess rules that conflict with Polylang's own rewrite rules for handling languages.

The Solution: Review your .htaccess file. Ensure that any custom redirect rules you have added are placed above the standard WordPress rewrite rules. Polylang's rules are integrated into the WordPress block, so custom rules can sometimes override them and break language detection for the homepage.

General Troubleshooting Steps

If you encounter an unspecified error, always start with these steps:

1. Enable WP_DEBUG: Temporarily enable WordPress debugging by adding define( 'WP_DEBUG', true ); to your wp-config.php file. This will often reveal more specific error messages.
2. Conflict Test: Deactivate all plugins except Polylang. Switch to a default WordPress theme like Twenty Twenty-Four. If the error disappears, reactivate your plugins and theme one by one to find the conflict.
3. Re-save Permalinks: Go to Settings > Permalinks and click "Save Changes." This refreshes the rewrite rules and can resolve many routing issues.

By understanding the root causes of these common errors, you can more effectively diagnose and resolve issues, ensuring your multilingual site runs smoothly.