<?php if (isset($quantity_taxation_curr) && in_array($currency['code'], $quantity_taxation_curr)) { ?>

{% if isset(quantity_taxation_curr) AND in_array(currency['code'], quantity_taxation_curr) %}

{% if quantity_taxation_curr is defined and currency['code'] in quantity_taxation_curr %}

{% if quantity_taxation_curr is defined and 'code' in quantity_taxation_curr %}
...
{% endif %}