gistfile1.php

<?php

class StringRandomizer {

    public function process( $text ) {
        return preg_replace_callback('/\{(((?>[^\{\}]+)|(?R))*)\}/x', array( $this, 'replace' ), $text );
    }

    public function replace( $text ) {
        $text = $this->process( $text[ 1 ] );
        $parts = explode( '|', $text );
        $part = $parts[ array_rand( $parts ) ];
        return $part;
    }

}

$randomizer = new Randomizer( );
var_dump( $randomizer->process( "{This is my {spintax|spuntext} formatted string, my {spintax|spuntext} formatted string, my {spintax|spuntext} formatted string example.}" ) );