$ wp i18n make-pot . languages/my-plugin.pot

$ wp i18n make-mo movie-library-hi_IN.po languages

array_diff()

How can we set the info selected by user and remove the user that is unselected in metabox?

We are only getting the selected ids and not what is unselected, for that we can get previously selected terms, compare them with currently selected and remove the ones that are not present in current.

For this, I used PHP array_diff() function,

Compares array against one or more other arrays and returns the values in array that are not present in any of the other arrays.

First we get the selected ids and create terms

$all_people = array_merge( $directors, $producers, $writers, $actors );
$terms = [];
// Create array of terms to be added now.
		foreach ( $all_people as $person_id ) {
			$person      = get_post( $person_id );
			$term        = $person->post_name . '-' . $person_id;
			$term_exists = term_exists( $term, '_rt_movie-person' );
			// Create the term if it does not exists.
			if ( ! $term_exists ) {
				wp_insert_term( $term, '_rt-movie-person', [ 'slug' => $term ] );
			}
			$terms[] = $term;
		} // end foreach

Then we get the terms selected before

// Get previous terms.
		$old_terms = wp_get_post_terms( $post_id, '_rt-movie-person', [ 'fields' => 'slug' ] );

Compare the both using array_diff() and get terms which are not in the current but were there in previous

// Get unselected Terms.
		$unselected_terms = array_diff( $old_terms, $terms );

Finally remove the relationship between terms and out post

		wp_remove_object_terms( $post_id, $unselected_terms, '_rt-movie-person' );

This way, the term relationship will get deleted when unselected in the metabox

WPDB – standard way to interact with WordPress database

wpdb is a class provided by WordPress that has functions to handle database queries without having to write raw SQL.

• It is used so we can query the wordpress database without having to write raw SQL queries.
• Create an abstraction layer over the database.

• Common methods
  1. insert() : insert data into a table
  2. prepare() : prepares sql query to avoid sql injection
  3. update() : to update data in table
  4. delete() : to delete data