SKaero thank you for your reply, I have read your posts, the functionality really was removed in 1.1 versions.
As I understood in the "program/lib/Roundcube/rcube_storage.php" the class "rcube_storage" has
variable "public static $folder_types = array('drafts', 'sent', 'junk', 'trash');" which is later foreached and the default folders are created.
So, if we will define additional folders (f.x. public static $folder_types = array('drafts', 'sent', 'junk', 'trash','folder2','folder2'); ),
and also in config file we will define that folders in such format "$config['folder1_mbox']='folder1'; $config['folder2_mbox']='folder2'; ", the problem should be solved.
But adding something in main functions (f.x. in 'program/lib/Roundcube/rcube_storage.php' ), are not good practice.
Taking into account that roundcube config file is not only config file, but also PHP parseable file,
it will be nice to add something only in config file, and don't touch the "program/lib/Roundcube/rcube_storage.php".
So, this one is more desirable solution, without touching any main function, and writing something only in config file:
add in config file these 4 lines:
// these lines will just append the existing array, when the config file will be parsed.
rcube_storage::$folder_types[]='folder1';
rcube_storage::$folder_types[]='folder2';
// these lines will work, because the final "$folder_types" variable already will contain the new defined folders
$config['folder1_mbox'] = 'folder1';
$config['folder2_mbox'] = 'folder2';
The example works on my server.