[Xposed Framework Modules] ChokingHazard91:
When this module first was released, I installed on my Galaxy Note 4 (N910F) running the stock Touchwiz ROM. It did work right away. But a few weeks ago I have switched from stock to Emotion AOSP 23.1. On Emotion it took me quite some tweaking and troubleshooting to get it work. FYI, I am using Nova Launcher and since I am using Emotion ROM, I also have an app called Rom Control. They both have settings to change button behavior. While tweaking those settings, I came the point to the point where I am now: the Assistant shows up in any app but on my homescreen Google opens up first and when I close Google the Assistant shows up. That means I'm not done with tweaking, and I'm not sure in what order I changed my settings to be where I am now, but I'll explain what I did in Nova and in Rom Control. If you use one of those apps (or any other app to change button behaviour), you may need to look into those settings. Those are the apps causing me some trouble.

If you get the language error, you need to do something else first.

Device language/AppLocale/AppSettings

So after installing the module, the assistant showed the language error. In this thread I saw that many people are having this error. As far as I know, if your system language isn't set to English the assistant won't work. I'm Dutch, so my system language is set to Dutch. Obviously you can change it English, but if you (like myself) don't want your whole device to be in English, you can use a Xposed module called AppLocale. AppLocale allows you to change the language of an app, without changing the system language. Setting the language of the Google app to English, might solve that issue. You can do the same with the Xposed module AppSettings, but since I only needed to change the language, I chose AppLocale. Before changing the language, I cleared the Google's cache and rebooted my device. After rebooting, the Google app was set to English, but that's where it really started..

Nova Launcher

After rebooting my phone I noticed that instead of the Assistant, nothing happened. That was weird, because the Assistant did show the language error.

Nova has an option to put a searchbar on your homescreen. I noticed that when I was holding the home button, the word 'Searching' showed up in that searchbar. So although it seems like nothing was happening, something actually did. I wanted to check the settings in the Google app but I tapped the app drawer it didn't open. I pressed my home button and tapped the app drawer again and it did open. In my recent app list I saw that Google was the last active app.

I opened up the Nova Settings to look for something causing this issue. At first I thought it had to do with the Search as overlay-setting. Enabling that setting shows an overlay instead of the full Google app during a search. I'm not sure if it was enabled or disabled that that moment, right now it doesn't change a thing, but you might wanna check that setting.

Nova also has a setting to change the home button behavior. Now I have it set to None, but I think it was set to Search, since Nova's searchbar did display 'Searching' when holding the home button. It didn't solve the problem for me personally, something else was causing it. You can set the home button behavior to Search, Voice Search or Google Now (and a lot of other options including None). Try and play with those settings, it might help.

Rom Control

As I said, I also have Rom Control installed. Because my Note has hardware keys, I can change the behaviour of them. The long-press action was set to None. One of the available options is Search Assistant. So I changed it from None to Search Assistant, long-pressed the home button and there it was! The Assistant showed up :) And I wasn't even on my homescreen, so I was glad it finally worked out.

But unfortunately, while I was holding the home button on my homescreen the Google app showed up. Still not wat I expected but hey, that's better than nothing. I pressed the back button to go back to my homescreen, and the Assistant was there. Strange..

So I opened a random app, long-pressed the home button again and the Assistant showed up. I closed the app and tried it again on my homescreen and once again the Google app showed up. So I closed Google and the Assistant was back.

And that's the point where I'm at right now. The Assistant opens in any app, working as expected, but on my homescreen Google comes first. Because the issue is on my homescreen only, I'm quite sure Nova is causing that.

So for everybody having problems with the Assistant not showing up, check any app that controls button behavior. It has almost solved the problem for me :)