The solution to put polylang switch side by side of the logo WordPress.

To use this tutorial, you need to find the current hearder.php file of your WordPress theme. (for example MH Magazine lite theme the header.php file is includes/mh-custom-functions.php)

first you need le the logo float to left. add the code to the style.css

line 110:    .mh-site-logo { padding: 20px; overflow: hidden; float: left;}

second you need add the fellowing code to the WordPress control panel ->Customizing ->Additional CSS

.hearderLanguange {
  margin-left: 75%;
  padding: 25px;
}
.lang-item {
  list-style: none;
}

Now you need go to the header.php file (in my case includes/mh-custom-functions.php). Insert the polylang short code into it.

echo '<div class="hearderLanguange">';
	pll_the_languages(array(//不顯示當前語言的旗子 show flag, not show name, hide current
		'show_flags'    => 1,
		'show_names'    => 1,
		'hide_current'  => 0,
	)); 
echo '</div>';

Reference: https://polylang.wordpress.com/documentation/documentation-for-developers/functions-reference/