I have setup configuration lang to ja_JP in iink 1.5.1,
and put assets(myscript-iink-recognition-text-ja_JP),
but Japanese Yoon (diphthong) cannot be recognized.
thank you for contacting us and your question.
This is currently a limitation of the technology, that in the absence of more context (i.e. characters before and after) confuses the second character with small and big size. This is something we are working to improve, but cannot commit when it will be done.
Meanwhile, our recommendation is to avoid recognizing "isolated characters" but instead recognize sentences.
Also, as the "small character" often appears as second candidate, you can export as JIIX and look for the other word and character candidates, and propose these to the user, so that he can update the result accordingly.