Hy there!
I found 2 bugs in ..administrator/components/com_virtuemart/views/coupon/view.html.php (line 127 and 142)
->join('LEFT', $db->quoteName('#__virtuemart_products_en_gb', 'vmpegb') . ' ON (' . $db->quoteName('vmp.virtuemart_product_id') . ' = ' . $db-
should be
->join('LEFT', $db->quoteName('#__virtuemart_products_' . VmConfig::$vmlang, 'vmpegb') . ' ON (' . $db->quoteName('vmp.virtuemart_product_id') . ' = ' . $db-
->join('LEFT', $db->quoteName('#__virtuemart_categories_en_gb', 'vceg') . ' ON (' . $db->quoteName('vmc.virtuemart_category_id') . ' = ' . $db-
should be
->join('LEFT', $db->quoteName('#__virtuemart_categories_' . VmConfig::$vmlang, 'vceg') . ' ON (' . $db->quoteName('vmc.virtuemart_category_id') . ' = ' . $db-
I'm using latest version of VM (3.8.4 10335) but this bug in (3.8.0.10319) too.