Why doesn't $request->getLocale() return the correct locale any more (since v.4.3)?

Sorry, but the problem persists. I not only tried all the steps in the documentation, but also the tutorial above. Working app based on CI 4.2.x is at https://ccpdemo2.ozar.net - it can be tested by selecting a language from the dropdown in the right hand side of the top navbar. When all the code in this app is copied over to CI 4.3.x, it breaks and language selection menu always takes the user to an English page. 

May I request, those who assert no such problem exists, describe all the steps to reproduce a working solution testing also with the Safari browser?

Can't do withouts:

The URLs to be tested need to be created using routes that will reside in the below route groups.

PHP Code:

$routes->group('{locale}/cp', [], function($routes) {
....
}  


or

PHP Code:

$routes->group('{locale}/admin', [], function($routes) {
....
} 


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