If it does not help, I need more information on your site by sharing the debug info. If you don’t know how to share the debug info, please follow this article https://wpml.org/faq/provide-debug-information-faster-support/
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Hi Long,
Thanks for your follow up. Here above the debug info. I'd rather not uninstall plugins, use beta versions or go back to old WordPress version as it may affects other elements of my site. Let's take a good look at what is happening first and try to understand the root of the problem.
I have deactivated ther plugin "WPML String Translation" and the time to switch from one language to another has become normal. I imagine that "WPML String Translation" is necessary. Do you have a fix for this?
According to the debug info, I do not see any issue. Recently, we received some performance issue reports that are related to the WPML String Translation plugin as in the documentation I shared above. You can copy your site to a staging site and apply the workaround there to prevent affecting your live site and see if it helps.
Issue is fixed with timing (I have removed the strings category, tag etc that where in the "Default" textdomain and the speed to switch became normal).
I have also another problem with many of my translations staying with the status "In Progress" despite having Completed the translation and seen "successful" when pressing "Complete" in the advanced editor.