Source

File: wp-includes/customize/class-wp-customize-date-time-control.php

public function get_timezone_info() {
		$tz_string     = get_option( 'timezone_string' );
		$timezone_info = array();

		if ( $tz_string ) {
			try {
				$tz = new DateTimezone( $tz_string );
			} catch ( Exception $e ) {
				$tz = '';
			}

			if ( $tz ) {
				$now                   = new DateTime( 'now', $tz );
				$formatted_gmt_offset  = $this->format_gmt_offset( $tz->getOffset( $now ) / 3600 );
				$tz_name               = str_replace( '_', ' ', $tz->getName() );
				$timezone_info['abbr'] = $now->format( 'T' );

				$timezone_info['description'] = sprintf(
					/* translators: 1: Timezone name, 2: Timezone abbreviation, 3: UTC abbreviation and offset, 4: UTC offset. */
					__( 'Your timezone is set to %1$s (%2$s), currently %3$s (Coordinated Universal Time %4$s).' ),
					$tz_name,
					'<abbr>' . $timezone_info['abbr'] . '</abbr>',
					'<abbr>UTC</abbr>' . $formatted_gmt_offset,
					$formatted_gmt_offset
				);
			} else {
				$timezone_info['description'] = '';
			}
		} else {
			$formatted_gmt_offset = $this->format_gmt_offset( intval( get_option( 'gmt_offset', 0 ) ) );

			$timezone_info['description'] = sprintf(
				/* translators: 1: UTC abbreviation and offset, 2: UTC offset. */
				__( 'Your timezone is set to %1$s (Coordinated Universal Time %2$s).' ),
				'<abbr>UTC</abbr>' . $formatted_gmt_offset,
				$formatted_gmt_offset
			);
		}

		return $timezone_info;
	}