How to use this below code to show other store language?
$store_language = $this->getChildHtml('store_language');
I am not sure not sure 100% about your question.
May be your want to call language dropdown at any phtml at frontend by $this->getChildHtml('store_language').
And code may be not works calling phtml's block
class is not parent block of store_language block class.
If you want to call any where at frontend area then you try this
echo $store_language = $this->getBlockHtml('store_language');
or call store language by create block:
echo $this->getLayout()->createBlock('page/switch"')->setTemplate('page/switch/languages.phtm')->toHtml();