使用php的wordpress自定义主题

I need a help in WordPress custom theme using PHP development, I was created language dropdown with images and in configure with Gtranslator Plugin, it`s work properly but when I select other language flag can't change in Dropdown. my Code is given below:

<li class="dropdown">
    <a href="JavaScript:void(0)" class="dropdown-toggle" data-toggle="dropdown"><img class="lang_icon" src="<?php echo get_stylesheet_directory_uri();?>/images/usaicon.png"> 
        <i class="fa fa-angle-down" aria-hidden="true"></i>
    </a>
    <ul class="dropdown-menu dropdown_language">
        <li><a onclick="doGTranslate('en|en')" href="JavaScript:void(0)">
            <img class="lang_icon" src="<?php echo get_stylesheet_directory_uri();?>/images/usaicon.png">
            </a>
        </li>
        <li id="cn"><a onclick="doGTranslate('en|zh-CN')" href="JavaScript:void(0)">
                    <img class="lang_icon" src="<?php echo get_stylesheet_directory_uri();?>/images/chinaicon.png">
                    </a>
        </li>
        <li><a onclick="doGTranslate('en|es')" href="JavaScript:void(0)">
            <img class="lang_icon" src="<?php echo get_stylesheet_directory_uri();?>/images/mexiconicon.png">
            </a>
        </li>
    </ul>
</li>