If the index.php discovers `$_POST['dynamic_locale']` is set (Which happens when a form has done a submit with one of the imputs named `'dynamic_locale'` it will set the language to that value. This is how the dynamic_locale plugin works--you select a language and a submit is done with the appropriate parameters.
So your could put a button on your form with the following:
`
<form name=zenphotolink action="http://domain.com/zenphoto/index.php" method="post">
<input type="hidden" name="dynamic_locale" value="en_US"/>
<input type="submit" value="Photos" />
</form>
`
for the English one. I'll leave the Polish version to you--I am not fluent
Cookies seem really tricky. I have not found how to set a cookie for zenphoto from outside of the zenphoto folders.