Wordpress: Use method="post" for multiple language selection

I'm building a website that has dual languages with two flags as an entry page. I'm planning on using <form method="post"> around the flags so the user can select the language they want.

Then on the following pages I want to use something like:

<?php
if( $_POST['language']=='uk' ){
    echo $uk;
}elseif( $_POST['language']=='french' ){
    echo $french;}
?>

So on clicking the flag, they have selected the language they want. Will that only work on the next page after they have clicked the flag or can they carry on navigating to different pages and it still pick up what language was selected?

If that doesn't work, how else can it be done?

UPDATE:

I don't think I made it clear before that I'm using Wordpress, which apparently doesn't like $_SESSION.

I have this on a template called region.php to submit the language selection:

    <form action="<?php the_permalink(); ?>/home" name="region" method="post">              
        <div id="uk">
            <a href="javascript:document.region.submit()" name="UK">
                <img style="margin-bottom:10px;" src="<?php bloginfo('stylesheet_directory'); ?>/images/-uk.png" width="259" height="160" alt="UK" />
            </a>
            <h1 style="color:black!IMPORTANT;">Enter United Kingdom site</h1>
        </div>

        <div id="world">
            <a href="javascript:document.region.submit()" name="World">
                <img style="margin-bottom:10px;" src="<?php bloginfo('stylesheet_directory'); ?>/images/
world.png" width="258" height="160" alt="
Rest of the World" />
            </a>
            <h1 style="color:black!IMPORTANT;">Enter Rest of the World site</h1>                    
            </div>  
    </form>

What do I need to put on every other template to check what language was selected? To help with the example if UK has been selected then it can just echo "UK", if the rest of the world was selected then it can just show "World".

This needs to work across several pages so if they goto the about page it checks the language, then if they navigate to the contact page it checks the language again - all that has to come from the initial language selection.

Solution

Answers

Firstly, for adding regional / multilingual support to a wordpress site there is no better alternative than this plugin: http://wpml.org/. It has a cost associated with it, but its not prohibitive (you pay for awesome support).

Secondly, You cannot use $_SESSION by default. WP is stateless by design. That said there are tons of plugins and tutorials online for getting this functionality.

Code stuff

Your original form html had no inputs. It was a form that submitted nothing. This form has two submits named the same thing location. So whichever button is clicked will submit its value against the $_POST['location'].

<form action="<?php the_permalink(); ?>/home" name="region" method="post">              
    <div id="uk">
        <input type="submit" name="location" value="UK" />
        <img style="margin-bottom:10px;" src="<?php bloginfo('stylesheet_directory'); ?>/images/uk.png" width="259" height="160" alt="UK" />
        <h1 style="color:black!IMPORTANT;">Enter United Kingdom site</h1>
    </div>

    <div id="world">
        <input type="submit" name="location" value="World" />
        <img style="margin-bottom:10px;" src="<?php bloginfo('stylesheet_directory'); ?>/images/world.png" width="258" height="160" alt="Rest of the World" />
        <h1 style="color:black!IMPORTANT;">Enter Rest of the World site</h1>                    
    </div>  
</form>

Write a wordpress action to handle the post. Add this to your theme's functions file. look at http://php.net/manual/en/function.setcookie.php for setcookie docs.

function set_location_cookie()
{
    if(isset($_POST['location']))
    {
        setcookie('location', $_POST['location'], time()+1209600);
    }
}
add_action('init', 'set_location_cookie');

Then, anywhere you want to know the location:

<?php echo $_COOKIE["location"]; ?>

ADDITIONAL INFO

I initially clicked UK to start with and this set the cookie, I then went back and clicked World but that didn't copy over the cookie with world, it just showed UK again. Is it possible to wipe over the cookie each time a different selection is made?

So this is an issue regarding how cookies work at a technical level:

When the browser does this [requests a site], it will look on your machine for a cookie file that [your site] has set. If it finds a cookie file, your browser will send all of the name-value pairs in the file to [the] server along with the URL. If it finds no cookie file, it will send no cookie data.

The new cookie data is not initially sent, b/c it inst until after the request has been sent from your browser to the server that the new cookie data is saved and available for sending with the request.

How do you make this work then? redirect after a successful set cookie event.

function set_location_cookie()
{
    if(isset($_POST['location']))
    {
        // Set Cookie
        setcookie('location', $_POST['location'], time()+1209600);
        // Reload the current page so that the cookie is sent with the request
        header('Location: '.$_SERVER['REQUEST_URI']);
    }
}
add_action('init', 'set_location_cookie');

Also is it possible to use the images of the flags as the submit buttons? Yes, use CSS to style your input buttons.

Add an id to each input: id="uk-button" and id="world-button"

CSS:

#uk-button {
    background-image: url(uk-flag.png);
    background-size: 100%;
    background-repeat:no-repeat;
}
#world-button {
    background-image: url(world-flag.png);
    background-size: 100%;
    background-repeat:no-repeat;
}