Language changes after placing an order

[sandomatyas]

I manage a multilanguage shop with VM 3.0.19.6.
The default language is Hungarian and the second language is English.
When I switch to English and place an order the thank you page switches back to Hungarian but only the VirtueMart related parts (VM categories module, currencies module etc) not the Joomla menus, Joomla modules, etc.
The url contains the right lang parameter: index.php?option=com_virtuemart&view=cart&lang=en
I tried with two different sites.
Could you help me with this please?

[jjk]

Might be the problem discussed here: http://forum.virtuemart.net/index.php?topic=136543.msg478022#msg478022
In my case I currently have to disable my 'Piwik for VM' plugin in order to avoid language switching problems.