wp_timezone_choice() WordPress Function

function wp_timezone_choice( $selected_zone, $locale = null ) {
	static $mo_loaded = false, $locale_loaded = null;

	$continents = array( 'Africa', 'America', 'Antarctica', 'Arctic', 'Asia', 'Atlantic', 'Australia', 'Europe', 'Indian', 'Pacific' );

	// Load translations for continents and cities.
	if ( ! $mo_loaded || $locale !== $locale_loaded ) {
		$locale_loaded = $locale ? $locale : get_locale();
		$mofile        = WP_LANG_DIR . '/continents-cities-' . $locale_loaded . '.mo';
		unload_textdomain( 'continents-cities' );
		load_textdomain( 'continents-cities', $mofile );
		$mo_loaded = true;
	}

	$zonen = array();
	foreach ( timezone_identifiers_list() as $zone ) {
		$zone = explode( '/', $zone );
		if ( ! in_array( $zone[0], $continents, true ) ) {
			continue;
		}

		// This determines what gets set and translated - we don't translate Etc/* strings here, they are done later.
		$exists    = array(
			0 => ( isset( $zone[0] ) && $zone[0] ),
			1 => ( isset( $zone[1] ) && $zone[1] ),
			2 => ( isset( $zone[2] ) && $zone[2] ),
		);
		$exists[3] = ( $exists[0] && 'Etc' !== $zone[0] );
		$exists[4] = ( $exists[1] && $exists[3] );
		$exists[5] = ( $exists[2] && $exists[3] );

		// phpcs:disable WordPress.WP.I18n.LowLevelTranslationFunction,WordPress.WP.I18n.NonSingularStringLiteralText
		$zonen[] = array(
			'continent'   => ( $exists[0] ? $zone[0] : '' ),
			'city'        => ( $exists[1] ? $zone[1] : '' ),
			'subcity'     => ( $exists[2] ? $zone[2] : '' ),
			't_continent' => ( $exists[3] ? translate( str_replace( '_', ' ', $zone[0] ), 'continents-cities' ) : '' ),
			't_city'      => ( $exists[4] ? translate( str_replace( '_', ' ', $zone[1] ), 'continents-cities' ) : '' ),
			't_subcity'   => ( $exists[5] ? translate( str_replace( '_', ' ', $zone[2] ), 'continents-cities' ) : '' ),
		);
		// phpcs:enable
	}
	usort( $zonen, '_wp_timezone_choice_usort_callback' );

	$structure = array();

	if ( empty( $selected_zone ) ) {
		$structure[] = '<option selected="selected" value="">' . __( 'Select a city' ) . '</option>';
	}

	foreach ( $zonen as $key => $zone ) {
		// Build value in an array to join later.
		$value = array( $zone['continent'] );

		if ( empty( $zone['city'] ) ) {
			// It's at the continent level (generally won't happen).
			$display = $zone['t_continent'];
		} else {
			// It's inside a continent group.

			// Continent optgroup.
			if ( ! isset( $zonen[ $key - 1 ] ) || $zonen[ $key - 1 ]['continent'] !== $zone['continent'] ) {
				$label       = $zone['t_continent'];
				$structure[] = '<optgroup label="' . esc_attr( $label ) . '">';
			}

			// Add the city to the value.
			$value[] = $zone['city'];

			$display = $zone['t_city'];
			if ( ! empty( $zone['subcity'] ) ) {
				// Add the subcity to the value.
				$value[]  = $zone['subcity'];
				$display .= ' - ' . $zone['t_subcity'];
			}
		}

		// Build the value.
		$value    = implode( '/', $value );
		$selected = '';
		if ( $value === $selected_zone ) {
			$selected = 'selected="selected" ';
		}
		$structure[] = '<option ' . $selected . 'value="' . esc_attr( $value ) . '">' . esc_html( $display ) . '</option>';

		// Close continent optgroup.
		if ( ! empty( $zone['city'] ) && ( ! isset( $zonen[ $key + 1 ] ) || ( isset( $zonen[ $key + 1 ] ) && $zonen[ $key + 1 ]['continent'] !== $zone['continent'] ) ) ) {
			$structure[] = '</optgroup>';
		}
	}

	// Do UTC.
	$structure[] = '<optgroup label="' . esc_attr__( 'UTC' ) . '">';
	$selected    = '';
	if ( 'UTC' === $selected_zone ) {
		$selected = 'selected="selected" ';
	}
	$structure[] = '<option ' . $selected . 'value="' . esc_attr( 'UTC' ) . '">' . __( 'UTC' ) . '</option>';
	$structure[] = '</optgroup>';

	// Do manual UTC offsets.
	$structure[]  = '<optgroup label="' . esc_attr__( 'Manual Offsets' ) . '">';
	$offset_range = array(
		-12,
		-11.5,
		-11,
		-10.5,
		-10,
		-9.5,
		-9,
		-8.5,
		-8,
		-7.5,
		-7,
		-6.5,
		-6,
		-5.5,
		-5,
		-4.5,
		-4,
		-3.5,
		-3,
		-2.5,
		-2,
		-1.5,
		-1,
		-0.5,
		0,
		0.5,
		1,
		1.5,
		2,
		2.5,
		3,
		3.5,
		4,
		4.5,
		5,
		5.5,
		5.75,
		6,
		6.5,
		7,
		7.5,
		8,
		8.5,
		8.75,
		9,
		9.5,
		10,
		10.5,
		11,
		11.5,
		12,
		12.75,
		13,
		13.75,
		14,
	);
	foreach ( $offset_range as $offset ) {
		if ( 0 <= $offset ) {
			$offset_name = '+' . $offset;
		} else {
			$offset_name = (string) $offset;
		}

		$offset_value = $offset_name;
		$offset_name  = str_replace( array( '.25', '.5', '.75' ), array( ':15', ':30', ':45' ), $offset_name );
		$offset_name  = 'UTC' . $offset_name;
		$offset_value = 'UTC' . $offset_value;
		$selected     = '';
		if ( $offset_value === $selected_zone ) {
			$selected = 'selected="selected" ';
		}
		$structure[] = '<option ' . $selected . 'value="' . esc_attr( $offset_value ) . '">' . esc_html( $offset_name ) . '</option>';

	}
	$structure[] = '</optgroup>';

	return implode( "\n", $structure );
}