Hi Nedim,
The sample skin is called a sample skin because it i just that: a sample. It is a sample of my modules, and not of the core modules, so as default there is no support for the core language selector, instead they only support my own language selector ;).
Having said that, of course the sample skin is just a skin, so you can easily fix that yourself. Just open one of the html files that you are useing, and change the token [MLLANGUAGESELECTOR] (which is the token for my language selector) with [LANGUAGE] (the token for the core language selector), and reparse your skin package.
You will find a lot information on how to work with skins in the DNN Skinning Documentation, which is part from the documents download at www.dotnetnuke.com.
BTW, if you want search engines to find the other languages of your site, you are better off by using my language selector, as it allows you to use hyperlinks, which can be followed by search engines (see how that works on my site, i have a menu language selector at the top of my page, and a hyperlink selector at the bottom.)
Cheers,
Erik