There are 2 web applications, ours and the other team. The other team's web app is http://otherteam.com and our application is http://myteam.com
On http://otherteam.com webpage, they have an href link pointing to our page which is http://myteam.com/config?lang=en. When our web application(actually Marionette AppRouter's task) receives that kind of route or path, it will parse it and set the language configuration and then we have a code to redirect the user to the final webpage which is http://myteam.com/landingpage
The code that we are using is
Backbone.history.navigate('landingpage', {replace: true});
to redirect the user to the final destination.
Unfortunately, when user clicks Back button of the browser, it doesn't go back to http://otherteam.com. It will go back to http://myteam.com/config?lang=en which is still our own application. What happens is that the Marionette app router will parse it again similar to how I described it above. The user will just be brought back to http://myteam.com/landingpage
So I changed
// Backbone.history.navigate('landingpage', {replace: true})
and now I'm using
history.replaceState({}, '', 'landingpage');
When I click Back button, the url on the top bar beocmes http://myteam.com/config?lang=en, but it doesn't reload our landingpage anymore which is good. However, nothing happens to the page until I click Back button again. After making the second click on the Back button, I'm back to http://otherteam.com which is great but I had to click the Back button twice.
The problem is you are redirecting the user from the /config?lang=en to another page, so when you click back, they land on the previous page and are then redirected back to the landing page again.
The simplest solution here would be for otherteam.com to link to your landing page and pass the params to be consumed there - http://myteam.com/landingpage?lang=en. Redirecting the user multiple time is never a good idea, and almost always unnecessary.
Once you have received the lang config param, it could be an idea to save it to local storage so it can be retrieved wherever it is needed throughout your app.