Marco

Problem:
If you're experiencing a fatal error stating 'Uncaught Error: Call to undefined function mb_ereg_replace_callback()', it indicates that your server is missing the Multibyte String Extension, which is crucial for the WPML plugin to function correctly.
Solution:
We recommend installing the Multibyte String Extension on your server to resolve this issue. Additionally, ensure that your server meets all the minimum requirements specified by WPML.

If this solution does not apply to your case, or if it seems outdated, please open a new support ticket. We highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. For further assistance, you can also visit our support forum at WPML Support Forum.