Giannis

Problem:
The client needs to change the URL parameter on a site under development, but the current WPML settings do not support this change.
Solution:
We recommend reviewing the WPML documentation on Language URL format options to consider alternative URL configurations. You can find detailed guidance here: Language URL format options.

If this solution does not apply to your case, or if it seems outdated, we highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have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. Should you need further assistance, please do not hesitate to open a new support ticket at WPML support forum.