Pull Request resolves #45452.

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

The mod_articles_category module's truncate() method used PHP's strlen() which counts bytes, not characters. For multibyte strings like Chinese (UTF-8, 3 bytes per character), this caused incorrect length calculations. When introtext_limit was set (e.g., 30 characters), the function would compare byte lengths and fail to produce output.

Fixed by changing \strlen() to StringHelper::strlen() which wraps mb_strlen() for proper UTF-8 character counting.

Testing Instructions

1. Create an article with Chinese content (no spaces between characters)
2. Add mod_articles_category module to a page
3. Set "Show Introtext" to Yes and "Introtext Limit (characters)" to 30
4. Verify the introtext displays correctly (previously showed nothing)

Actual result BEFORE applying this Pull Request

Chinese introtext with introtext_limit set shows nothing/empty.

Expected result AFTER applying this Pull Request

Chinese introtext displays correctly truncated to the character limit.

Link to documentations

• No documentation changes for guide.joomla.org needed
• No documentation changes for manual.joomla.org needed