Chinese Iphone Keyboard
Which keyboard on the Iphone is recommended for the Duolingo Chinese curriculum?
I’m not 100% sure but I think Duo is using the Simplified characters although there has been a number of requests to use Traditional characters. But for the time being I recon you should install the Simplified keyboard.
It seems that Duolingo recognizes Traditional Chinese input. So you don't need to worry about that.
I have an Android phone so I am not familiar with iPhone.
For Duo, where possible you should get the one with Pinyin input and Simplified Chinese output.
If there are several types of Pinyin input (or several options in the keyboard settings), choose 全拼/Quanpin (as opposed to 双拼/Shuangpin).