This is the technical support forum for WPML - the multilingual WordPress plugin.
This thread is resolved. Here is a description of the problem and solution.
Problem: I am trying to an add item to basket, then add another and go to chekout in French. Instead, I got unexpected switching from French language to Russian
Solution: In this case the most probable cause for the issue is an outdated cache memory, which is probably in your browser so clients won't see the problem.
However I recommend you to contact your hosting providers and ask them to flush any cache memory that might exists at server level.