Datatrans Interface (Redirect) is in the default language instead of Drupal current language

Problem/Motivation

When we finalize our checkout, we are redirected to Datatrans Gateway.
This Gateway is in the Default Language of Datatrans (configured in Datatrans), the previous (before redirect) Drupal current language is not used.

Proposed resolution

Add the language GET parameter to the Drupal\commerce_datatrans\PluginForm\DatatransForm & used the Drupal UI language (langcode) as value.

Completed tasks

• Write a patch.

Remaining tasks

• Review and commit.

User interface changes

The redirection will be i18n using the Drupal UI language if available.

API changes

None.