"Tracking Click-Throughs" option in mailings generates 404 links when using multi-language with path prefix

This occurred in a Drupal environment with multiple languages and the following configuration:

• Languages in Drupal:
  • English (activated)
  • German (activated, default)
• Languages in CiviCRM:
  • Default language: English
  • available: German, English
  • Inherit CMS language: yes

Conditions under which the erroneous behavior can be reproduced:

• Mailing language: English
• UI language: German
• language prefix in the URL: none or "de"

or:

• Mailing language: German
• UI language: English
• language prefix in the URL: none or "en"

ergo: Using a UI language different from the mailing language and having path prefixes for language detection.

The result is links to the tracking script being prefixed with the language code of the UI language, like so: https://example.org/de/sites/all/modules/civicrm/extern/url.php?u=123&qid=12345

which is producing a 404 as obviously the path to the script file is not valid due to the language prefix.

Apparently, this code in CRM/Mailing/BAO/TrackableURL.php:93 is where the URL is constructed, but with userFrameworkResourceURL being prefixed with the language code:

$redirect = $config->userFrameworkResourceURL . "extern/url.php?u=$id";