Enabling encryption on a Huawei Y5 II?

[AC Question]

I'm not good at this, so apologies if I use the wrong terminology.

The "Encrypt phone" option in the Settings menu on my phone is missing -- according to several forum posts, it's disabled by default on Huawei's ROM. Someone suggested to install a third-party Android launcher app. I did so, and gained access to the hidden encrypt phone menu, however, the option (the button) is greyed out.

1. Would rooting the phone and installing a custom ROM enable an "encrypt phone" option? If so, which method should I use to root it? And which custom ROM should I install? Would replacing the custom Huawei EMUI ROM with the Android 5.0 Lollipop stock ROM be helpful for enabling the option, for example?

2. How can I tell whether the phone is possibly already encrypted?

3. Some forum posts mention connection the phone via USB to my computer (Windows 7) and somehow, via a terminal command, force an encryption process. Does anyone know how to do that?

Data about the phone:

Model: HUAWEI CUN-L21
Version: CUN-L21C577B115, Android 5.1, EMUI 3.1

Let me know if you need more information. I'd be so grateful for any advice!