URL Language Switching Problem

Hi, we have a shipment tracking page https://wwwdev2.egtexpress.com/en/tracking/. After entering a shipment number, there is a query string in the URL, e.g. ?shipment=AM9358434 – so the URL is https://wwwdev2.egtexpress.com/en/tracking/?shipment=AM9358434.

When I want to switch language on the tracking page without the query string, everything works right. However, once I am on the page with the query string, I can only switch to the second language in order. The third language offers the URL of the second language in the sequence.

So when I’m at https://wwwdev2.egtexpress.com/en/tracking/?shipment=AM9358434, only the URL of the second language in order, https://wwwdev2.egtexpress.com/cs/tracking/?shipment=AM9358434, is offered for the other languages.

But when I’m on https://wwwdev2.egtexpress.com/ru/tracking/?shipment=AM9358434, the URLs in the language switcher are correct, they just don’t contain the query string.

Any idea what the problem might be?