One page of SMS is equal to 160 characters of normal text. If your SMS goes beyond 160 characters, it becomes 2 pages. And subsequently 3 pages for more than 320 characters, and so on.

Yes, if your message is more than 160 characters it will be concatenated as a long SMS. Note that this feature to some degree depends on how the receiving phone responds to concatenated SMS.

Yes all the languages are supported. However for those special languages, you will need to specify that the message encoding is unicode when sending the message (please note that unicode messages reduces the character limits to 72 characters per page)