Change WordPress language based on user setting

Question

I want to change the language of my WordPress installation based on a choice the user can make in his profile (dropdown menu).

As I want to change frontend (prepared .mo files for the theme) and backend language I thought I could change the $locale variable and it would work out.

So I came up with the following code in my functions.php but that won´t do the job:

function change_lang() {
   get_currentuserinfo();
   $lang = get_user_meta($current_user->ID, 'user_lang');
   $locale = $lang[0];
   return $locale;
}
add_filter('locale', 'change_lang');

When I return the value of $locale, WP returns a simple NULL, nothing more. When I release the hook, the defined value from WP_LANG() is returned.

So, I am obviously wrong somewhere, but I can´t find where. Any hints?

Besides: I read this for inspiration and code, but I don´t want to have it as a plugin if possible.

Thanks in advance!

Edit: Fixed my code, but still no language change happens.

Answer 1

Your use of $current_user is a little wrong, you should include the global $current_user or assign it to a variable, or shorter and cleaner just get_current_user_id():

add_filter('locale', 'change_lang');
function change_lang( $locale ) {

   if( $lang = get_user_meta( get_current_user_id(), 'user_lang', true) ) {
       return $lang;
   }

   return $locale;

}

Answer 2

I had a similar problem in my plugin and nothing in here worked.

After days looking into it. I've realized that it is impossible to get the current user inside the filter 'locale'. Not even calling the global $user_locale.

Apparently the hook 'locale' is triggered before init, or anythig else.

After all i found out that I was loading my plugin text domain before setting the locale. So, calling it right after switch_to_locale() fixed the problem.

This worked for me:

function set_user_locale(){

   switch_to_locale(get_user_locale());

   load_plugin_textdomain( 'plugin-texdomain', false, dirname( plugin_basename( __FILE__ ) ) . '/languages' ); 

}
add_filter('init', 'set_user_locale');

Answer 3

Did you mean this option ?

If yes, then...

$user_locale = get_user_locale();
function change_userlang_by_userlocale($locale){
    global $user_locale;
    return $user_locale ? $user_locale : $locale;
}
add_filter('locale','change_userlang_by_userlocale');