Ability to ommit langcode for the selected fallback language

Problem/Motivation

The core Url language negotiator provides the ability to ommit the langcode for the selected fallback language. Here is the help text from the configuration form:

Language codes or other custom text to use as a path prefix for URL language detection. For the selected fallback language, this value may be left blank.

It would be great if this module supported this functionality as well. If the language code is left blank, the module uses the default langcode for the selected fallback language.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes