Wordpress built-in function to display international dates properly. Retrieve the date in localized format, based on timestamp.

date_i18n

$_evento = get_proximos_eventos(1);
$evento = $_evento[0];

$unixtimestamp_inicio 	= strtotime($evento['data_inicio']);
echo date_i18n('M', $unixtimestamp_inicio); // Abril

// Depending on your blog settings you will see the date displayed in your local format, for example: 15. november 1976.
echo date_i18n( get_option( 'date_format' ), strtotime( '11/15-1976' ) );