May well be Japanese course specific. I am on Android and checked on web also — same experience. I have an iPhone too though, so will check it out and report back.
In my experience with the Japanese course, there are no text prompts at all. Well, not in the main course. You do receive prompts when learning the Japanese alphabets, but these text prompts are specifically asking for the Romanised pronunciation.
I just started Japanese and on the web client for me I can type answers with my keyboard in Japanese mode just fine. Including submitting answers with kanji even though it hasn’t covered any yet
In my experience with the Japanese course, there are no text prompts at all. Well, not in the main course. You do receive prompts when learning the Japanese alphabets, but these text prompts are specifically asking for the Romanised pronunciation.