After you have enable the multilingual and configure the default and available languages, you may want to set a language switch in the front end site. 

All the Url, parameters and routing will be rendered by Kooboo automatically, what you need to do is providing a link where user can switch their language. 

SitePath

If you enable the SitePath option in the system setting, your language indicator is at the path, your switch may looks like below

<ul> 
<li><a href='/en/mypage'> English</a></li> 
<li><a href='/zh/mypage'> Chinese</a></li> 
</ul>

Lang Parameter

If you did not enable the Site Path, the language indicator will be set in the Url, to switch the language, you can use code below. 

<ul> 
<li><a href='/mypage?lang=en'> English</a></li> 
<li><a href='/mypage?lang=zh'> Chinese</a></li> 
</ul>