wpdb::determine_charset( string $charset, string $collate ): array

Source

public function determine_charset( $charset, $collate ) {
	if ( ( ! ( $this->dbh instanceof mysqli ) ) || empty( $this->dbh ) ) {
		return compact( 'charset', 'collate' );
	}

	if ( 'utf8' === $charset ) {
		$charset = 'utf8mb4';
	}

	if ( 'utf8mb4' === $charset ) {
		// _general_ is outdated, so we can upgrade it to _unicode_, instead.
		if ( ! $collate || 'utf8_general_ci' === $collate ) {
			$collate = 'utf8mb4_unicode_ci';
		} else {
			$collate = str_replace( 'utf8_', 'utf8mb4_', $collate );
		}
	}

	// _unicode_520_ is a better collation, we should use that when it's available.
	if ( $this->has_cap( 'utf8mb4_520' ) && 'utf8mb4_unicode_ci' === $collate ) {
		$collate = 'utf8mb4_unicode_520_ci';
	}

	return compact( 'charset', 'collate' );
}

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