Hello
I have checked now the differences between Joomsef version 3.7.0 and 3.7.1
When I replace the follwing code from the new version in joomsef.php:
if ((empty($code) || !JLanguage::exists($code))) {
(line 844)
with the code from the previous version:
if ($redir && (empty($code) || !JLanguage::exists($code))) {
(line 711)
the language will not be set to default when checking out, it remains in the selected language.
BTW: I don't agree with your comment:
// removed && $redir - it was not possible to switch language to main language
// on other page than homepage (let's see if it causes any other problem)
I never had problems in version 3.7.0