importing .vpl files (vpn tunnels) on mac
You can use the "FortiClientTools" application in Windows to import your .vpl configuration file. From there, you can export the configuration file to a newer type (4.3/5.0) that can be imported into newer versions of FortiClient. Exported config files that are encrypted will likely have a filename extension of .sconn; unencrypted config files should be appended with .conn.

If you need to import those config files into the newest version (5.2) of FortiClient, you can change the filename extension from .sconn or .conn to the newer format (.sconf; .conf). Once the extension has been changed, you can import that config file under the FortiClient menu -> Preferences -> General -> Restore.