Hello,
Most likely, the website performance suffers from the content you have added to your website. It may happen in case of too many plugins, large not optimized images or other resources. So we suggest users to remove unnecessary plugins, install some kind of JS & CSS optimizing plugins like Better WordPress Minify and caching plugin like WP Super Cache. Also, you can use GTmetrix tool to see what makes your website slow and optimize these parts of your website.
So, not only the WPML plugin is the cause of low performance.The choice is yours whether you want to try the “Polylang” plugin or WPML plugin.
Best Regards.