A few days ago I bought a new notebook without an operating system. I am planning to install Arch Linux and Windows 10, because sometimes at university you get software you have to use which can only be executed with Windows. Since it is a mobile device, I want to encrypt the drive or at least the Arch partitions. If there is an easy way to encrypt the Windows partitions too, I would do that, otherwise it would be no big problem for me to have no sensible data there. Could you explain me shortly (or detailed, if you like to do so) what I can do to encrypt both operating systems? I want to use GRUB as bootloader since I never tried to use Microsoft's bootloader for dualboot.
Typical Linux encryption solutions appear to be per block device: this means that you should probably look for separate solutions for each operating system. Arch Linux has documentation about how to do this (https://wiki.archlinux.org/index.php/Disk_encryption); it mentions that some options are loop-AES and dm-crypt.
I can't comment on the Windows part of your question, but I assume you will find a similar plethora of options.
Thing about TrueCrypt is that its development is discontinued, because of security problems with windows systems I think, I personally use VeraCrypt to encrypt, it is cross-platform I believe, and is very easy to use and similar to TrueCrypt.
I have pretty much exactly same setup as yours, but on Desktop, instead of notebook. I had some problems regarding grub on arch linux, I could not set it up, if you run into the same problem and if you have UEFI/GPT setup, I suggest you use systemd-boot(gummiboot) which works perfectly and is much simpler then grub(link - https://wiki.archlinux.org/index.php/Beginners%27_guide#UEFI.2FGPT).