Use a multilingual plugin like WPML, Weglott, Polyglot, or another, and you set up the language settings to use custom folders with the language code, e.g., yourdomain.com/en/. You may encounter an issue where opening a page on a staging site results in error 404. That can happen if the staging site permalinks are disabled.
There are three available solutions:
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Create the staging site in a subdomain
You can clone your WordPress website to a subdomain. If you do this, you will no longer run into any link structure issues, as the URL structure mimics the URL structure on the production website.
Change WPML language URL format.
You can switch the WPML language settings on your WP Staging staging site to URL-based language like yourdomain.com/?lang=en
You can change this under WPML > Languages.
Note: If you push the staging site back to live, you must revert this setting on the live site.
Activate post name permalinks.
You can try to activate post name permalinks on the staging site by following this article.
WPML Troubleshooting Options
After pushing or cloning your WordPress site with WP Staging, the WPML translations might not work as intended. The internal cache handling of WPML often causes that. Gladly WPML offers you a few powerful troubleshooting options that you can access to purge and refresh the WPML cache.
The information on this page is for advanced WPML users. If you are unsure what you are doing, please contact WML support before executing any WPML troubleshooting options.
You can open the WPML troubleshooting page from WPML > Support.
Click the link for troubleshooting.

Before executing any listed action from that options page, create a WordPress website backup.

In the table below, you see a description of the most important commands and possible use-case scenarios:
Command | When to use it |
Clear the Cache in WPML |
|
Remove ghost entries from the translation tables |
|
Fix element_type collation |
|
Fix WPML table collation |
|
Set language information |
|
Cleanup and optimize string tables |
|
Source:
https://wpml.org/documentation/support/wpml-troubleshooting-options/