I use the widget monetary in Qweb like this:
<span t-field="sale_order.amount_untaxed" t-field-options='{"widget": "monetary", "display_currency": "sale_order.company_id.currency_id"}'/>
But the output uses dot instead of coma as decimal point that my l18n settings are asking for.
100.50 € instead of 100,50 €