When you use our hosted signup page, you can submit an english page by adding the following URL suffix /portal/signup.html#/"Planvariants-Id"?language=en
If you use our hosted order portal, you can easily display an English translation of the order page with the URL suffix /portal/signup.html#/"Plan Variant ID"?language=en for your customers. You can also access a French order page with "?language=fr". You can translate the titles and headings of the respective languages in "Settings > Integration > Self-Service > Hosted Signup". These translations can also be output for other languages.
You can also prefill the country of the billing address with a URL query string. Several parameters are separated by"&" https://de.wikipedia.org/wiki/Query-String You can find a list of fields that can be pre-filled here:
fname, lname (First- and Last Name)
cname (Company Name)
pnum (Phone Number)
email (Email Address)
street, hnum (Street and House Number)
pcode, city (Postal Code and City)
aline1, aline2 (additional address lines)
country (Country as 2-letter ISO code)
vatid (VAT ID)
tag (A tag field that can be used to pass external id for example)
language (ISO code for languages, which also switches page language between German and English)
Further information can be found here: https://developer.billwerk.io/Docs/GettingStarted under the section "Hosted Customer Self-Service".
The two-digit ISO 3166-1 code is used for the country codes. You can find a list here: https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2 The code for the language (?language=) should be written in lower case, the code for the country capitalized. For regional languages use "-" and the country code.