[freebuju]

There's no such thing as internet permission. The only way to turn off this "juicy permission" is to not use any internet connection.

Though you can get away with firewall-ing any app you don't want connecting to the internet using apps such as netguard or afwall+.

Open source keyboards you've mentioned are probably your best bet if privacy is your main concern.

[jacob019]

Actually there is an internet permission.

    To perform network operations in your application, your manifest must include the following permissions:
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

source: https://developer.android.com/training/basics/network-ops/co...