Japanese mode has predictive text, English mode does not.There is a toggle to type in Japanese mode (default) or English mode (it's the second button from the bottom left).TL DR: It sort of works when you replace the input method's Japanese dictionaries with English versions pulled from a PS Vita (screenshots attached) but only in the Japanese locale and as soon as you type in a valid Japanese syllable, it'll display hiragana or katakana suggestions only (so that part must be built in), which makes it less useful as an English keyboard. I find predictive text useful on touch devices, so I wanted to see if it could be used for English words because the functionality is already there. Predictive text is important because Japanese has four different writing systems and text input is done phonetically through the Roman alphabet, so the system needs a way to translate those Roman letters to the appropriate kana or kanji character (For example, there are many characters that can represent the syllable 'ka' so predictive text allows you select which one you mean). I'm not sure how many were aware, but when you switch your device to Japanese, you get access to a predictive text keyboard.

Japanese keyboard predictive text