Add Japanese translation to "Typing issue for Mozc"

[utuhiro78]

Typing issue for Mozc
Please add Japanese translation after English messages.
I think some Japanese users don't understand English well.
They will close the page silently.

e.g.
Category / カテゴリー
category of typing issue / タイピング問題のカテゴリー

1. OOV: Out-of-vocabulary / 語彙がない
   e.g. "夕日" is not in the candidate list at all / "夕日" が候補リストにまったくない.