$Smarty.server.REQUEST_URI content is empty in some cases

Hello all.

First af all, thanks for greate work. Your app is awesome.

Now about my problem.
Our journal uses Open Journal Systems
There are several issues and submissions have been uploaded to the site. The content of our site is bilingual (Russian and English). To swith between languages we use languageSwitcher template.
To determine URI for translated submission $smarty.server.REQUEST_URI is used.
Here is my problem.
When the user browses the site internally (e.g. navigates from one view to another, or from any section of my site), it works just fine. In this case $smarty.server.REQUEST_URI contains the correct value and I can switch the language.
But if I want to navigate to a submission from an external resource (like doi.org) by the submission DOI, the $smarty.server.REQUEST_URI variable will be empty (I guess). And clicking on the language icon relays me to the main page of the site.
Please explain me how to resolve my problem.

My site is www.rm.tsnigri.ru