What's the difference between GPL licence and CECILL-2.1?

Question

These two licenses are for open-source code. Does the CECILL-2.1 give rights to sell the open source code without author notification, as it says in Article 5?

5.3 RIGHT OF DISTRIBUTION
In particular, the right of distribution includes the right to publish, transmit and communicate the Software to the general public on any or all medium, and by any or all means, and the right to market, either in consideration of a fee, or free of charge, one or more copies of the Software by any means. The Licensee is further authorized to distribute copies of the modified or unmodified Software to third parties according to the terms and conditions set forth hereinafter.

Does the GPL grant permission to the licensee to distribute the source code freely? Are they both copyleft?

Answer 1

Does the CECILL-2.1 give rights to sell the open source code without author notification

It is a characteristics of all open-source licences that the upstream authors don't need to be notified when someone exercises the rights received in the license. It can even be seen as one of the defining characteristics, because the license must not discriminate people who are unable to contact (all) upstream author(s).

Does the GPL grant permission to the licensee to distribute the source code freely?

Yes. The GPL even requires that you cannot charge extra for distributing the source code.

Are they both copyleft?

Yes, both licences mentioned are copyleft licences.