RedirectLanguage add the possibility to redirect url's without language parameter to url's with language parameter. It is useful if you change add language to url parameter in a Contao 2.11.X version. It is based on the official fix from https://github.com/contao/core/commit/22f4fe2128a1519a4c00b842fb2efd2078519cb9 .
Installation
Unzip the content of the zip-file to system/modules/redirectlanguage