Multiple language changes in extension section ends in a 404

**Affected version(s)**
User Manual

**Description**  
Multiple language changes in extension section  ends in a 404

**How to reproduce**  
1 open https://docs.contao.org/manual/de/erweiterungen/merger2/
2 select english in language switcher
3 select german in language switcher an you get 404 not found
