Pull Request for Issue #21132

Summary of Changes

Route is much stricter in 4.0. Getting twice lang in the url, i.e.$lang=xx-XX&lang=xx breaks routing.

Testing Instructions

Create a multilingual site with the multilingual sample data.
Make sure sef is on. Tested here with url rewriting.
Homes are category menu items per default.
Load frontend home and switch language via the language switcher.

Before patch

We should get urls of type
whatever/fr
whatever/en

Actual result

We get
/en?view=category&id=8
and
/fr?view=category&id=9

Also, If some article are associated and we have 2 not associated single menu items
The switcher flag for the language in use gives correctly
/en/modules-en-gb
but when switching to the other language, we get
/fr?view=article&id=13&catid=12

After patch

Urls are correctly displaying.

Note: we can't test now for Contacts as we have multiple errors, but it can be tested for single associated newsfeeds (their menu items NOT associated) AFTER merging #21140 OR using last instance of 4-0-dev (not nightly build).

For Newsfeeds categories as well as for Contacts categories, we have a fatal error (Cannot redeclare class) and therefore can't test.

@laoneo @franz-wohlkoenig