Billing form not translated

I have a website in 3 languages – English, Spanish and Portuguese. All translations seem to work fine, but the billing form is not translated.

Please see https://yourlondontutor.com/es/services/planificacion-del-itinerario/ and go through cart to checkout.

I can see those strings are translated in both .po files, how do I fix this to shows the form fields in the correct language