[Huawei P9 Plus Guides, News, & Discussion] zhuanyi:
I have recently acquired a P9 Plus (Chinese Version) and one of the issues with all of the Android phones sold in China is that they don't have Google services (Google in banned in China because of its refusal to comply with the Chinese internet regulations). There are ways you can install bits and pieces from the Huawei app store but it would be difficult to get all of the Google services together. There are ways already posted on XDA where you can install contact sync and app store one by one, but to me downloading through apkmirror (or any other site) could be a risk since those are uploaded by anonymous users and unless you can decompile the code and try to understand what's in those, it would be difficult to know if the apk is or is not doing something that are not designed for.

This guide assumes that you have unlocked bootloader and installed TWRP on it. Also I am not sure if you need to root the phone (which is pretty much for free once you had TWRP installed) but I had my phone rooted by the time I installed OpenGapps, obviously during this process you would have got the ADB drivers installed.

This process will wipe all user data, so please make sure you do a backup on your phone first.

First step is to download the installer zip to PC (or to SD card, I didn't have a spare SD card so I just download directly to PC), go to http://opengapps.org/, choose ARM64 (I know it is not actually ARM processor but somehow this package works, may be ARM and Kirin have compatible instruction set? That will sure make custom ROM development a lot easier!), 6.0 for OS version and choose the package you would like to have. I used nano but I am sure for other packages would work too.

Now go to TWRP on your phone. If you have downloaded the installer on your SD card you can just do Install -> select the zip and flash. I downloaded to my PC so I have to use the Sideload route, basically go to Advanced -> ADB sideload and simply do adb sideload FILE_NAME.zip (replace FILE_NAME with the actual OpenGapps package name you have downloaded). After that I originally tried to wipe caches and simply reboot but that didn't work for me.

So here is the trick, you will need to wipe Data and Internal Storage as well. I know, this sounds crazy but this is how it worked for me. If you managed to get other combinations to work feel free to suggest here as well.

What I did was I went to Wipe -> Advanced Wipe wiped Cache/Dalvik Cache, Internal Storage and Data (i.e., check everything except System and Micro SDCard) and then did a wipe.

After that, Reboot -> System.

Now once you are done with the set up, you will be greeted with an "uglier" version of the original UI (no fancy gold color!), but guess what, you should be able to see Google Play Store and you should be able to add Google accounts in Settings -> accounts.

For some reason I noticed if you try to add Google accounts you seem to be able to add one only (may be I overlooked something) so what I did was I went to the GMail app then go to Settings -> Add Account and that allows me to add the other Google accounts. Once you add a Google account on the GMail app it should be visible in other Google apps (App Store/Movies/Games, for instance) as well.

Any questions/better ideas feel free to post them below.