[Resolved] The Thai language version of my site is showing up with /th/th/ at the end

Problem:
The client reported an issue where the Thai language version of their website had a double extension in the URL (e.g., /th/th/), causing the page to break. Upon troubleshooting, the client found that disabling the 'Custom Permalinks' plugin resolved the issue, but deactivating it would affect many page URLs.

Solution:
We recommended the client to:
1. Ensure a full backup of the website and database.
2. Perform the following steps on a staging or development site:
- Deactivate all plugins except WPML and its addons to check if the issue persists.
- Clear all caches and resave the permalinks.
- Reactivate each plugin one by one, checking for the issue after each activation to identify any conflicting plugins.
- If the issue remains, repeat the steps using a default WordPress theme.
We also informed the client that the 'Custom Permalinks' plugin is on our compatibility list, but it has not been tested for a long time. We suggested contacting the plugin developer for further assistance if issues arise.

Please note that the solution provided might be outdated or not applicable to your case. If the issue persists, we recommend opening a new support ticket. We also highly recommend checking related known issues, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If you need further assistance, please contact us on the WPML support forum.