WPML Set Style
To set a language switcher on your site’s header, install the latest version of WPML or Polylang plugin and adjust the basic settings.
Go to Theme Options > Header Builder and click on Add Element and select language switcher in whichever section you want.
Click on edit and under General Settings, select your plugin.
Under style tab, you can customize each and every item you want.
Now, go to WPML > Languages and from the right side menu, in the Widget Language Switcher tab click on “Add a new language switcher to a widget area”.
In the new window, you can set the new main style that you want for a switcher.
Now, considering the main style of a switcher, you can adjust your main changes in the style tab in the header builder.