On one of my websites the option to update to the local language version is missing.
This is what I’m expecting to see
An updated version of WordPress is available. You can update to WordPress 4.9–en_GB automatically: This localised version contains both the translation and various other localisation fixes. You can skip upgrading if you want to keep your current translation. You can update to WordPress 4.9–en_US automatically: While your site is being updated, it will be in maintenance mode. As soon as your updates are complete, your site will return to normal.
But for this site I only had the option to do the non-localised language update.
How to install the en-GB version of WordPress?
in the root file wp-config.php I had
//define('WPLANG', ''); define ('WPLANG', 'en-GB');
I found that this is now deprecated. As of WordPress version 4.
To set the locale for the WordPress website the variable $locale is set accordingly within the file wp-config.php, found in the root of the website.
I replaced it with
//define('WPLANG', ''); //define ('WPLANG', 'en-GB'); $locale='en_GB';
and it worked!
Note the change from a hyphen to and underscore.
If you are interested in reading further about wplang and its deprecation these links may interest you.