When using WPML, you can add and customize language switchers in various areas of your site, including setting flag sizes. However, sometimes the flag sizes on the front-end might differ from your settings. This discrepancy is typically due to CSS styles or scripts from themes or plugins that override the image tag styling and alter the flag size.
You can add and customize language switchers to your site’s menus, widget areas, and footers through the WPML → Languages page.
When you enable flags in the language switcher, you also have the option to define their size.