Use $wpdb->prepare with parameter is array

prepare.php

// ref: http://wordpress.stackexchange.com/questions/110982/how-to-modify-this-wpdb-query-to-accept-an-array-of-post-statuses

// escape the values
// $filter is array of string
$filter = array_map( 'esc_sql', (array) $filter );
$filter = "'" . implode( "','", $filter ) . "'";

$rows = $wpdb->get_results(
    $wpdb->prepare(
        "SELECT * FROM language_table
        WHERE language_code=%s AND id IN (" . $filter . ") ORDER BY id",
        $language_code
    )
);