Have you considered GBoard? It is the official keyboard used in the stock Pixel OS. You are free to disable it's network access if you have privacy concerns. It has no issues.
Discussion
What about this? 
That notification appears for any keyboard app, it isn't specifically about GBoard.
You are free to disable internet access for the keyboard and it can't send anything out.
Ok. I think that's what I am going to do. Thank you!Maybe you've shared that before where do I disable the internet access fot it? May e that's why the Yandex and other keyboard wouldn't download my other language. If I forgot and did the internet disable thing.
When you download an app it gives you the choice to enable/disable on the install dialog.
Otherwise, go to Settings -> Apps -> All apps -> (the app you choose) -> Permissions -> Network
Ah ok. I already unchecked Network Permissions when I installed. Thank you, for confirming that's the same thing.