There is a problem with VM Invoice as the front-end PDF links on the webpage don't work with multi-language.

www.minuripsmed.ee/component/vminvoice/invoices/pdf/7490 <-- this link works
www.minuripsmed.ee/en/component/vminvoice/invoices/pdf/7490 <-- this link does not work

JoomSef version: 3.8.2
VM Imvoice: 2.0.27

No support?

Maybe I should ask my money back then?

Really unhappy here and business is suffering.

Hi,
Thank you for your report, we'll check the problem and let you know.
Please also try updating your JoomSEF to the latest version, maybe the issue has already been fixed.

Updating JoomSEF did not help.

The problem seems to be that there is no data saved to database on what are the user languages as JoomFish does not store languages on server. So every time the invoice is emailed to buyer or opened by buyer the email is defaulted to english.

I've just tested the multilanguage links for frontend PDF access with the following configuration and it works correctly on our test server:
Joomla 1.5.26
Joomfish 2.2.3
JoomSEF 3.10.2
VM Invoice 2.0.27

I've tried it with both Jfrouter enabled and disabled. So there's probably some problem with configuration on your server. Please post the screenshots of your JoomSEF configuration.
Also make sure that the plugin System - ARTIO JoomSEF is ordered as the first of your system plugins. If you have the System - Jfrouter plugin enabled, try disabling it and setting the configuration in JoomSEF's Configuration on the JoomFish tab.