It is not possible to enter Japanese directly into the Quartus II text editor.
By changing a simple setting, Japanese display is possible by copying and pasting from general-purpose text.
The setting method is explained below.

Setting method

1. Select Tools ⇒ Options ⇒ Text Editor ⇒ Fonts from the Quartus II main menu toolbar
2. Select any Japanese font from the Font field (MS Mincho, etc.)
3. Copy the Japanese input in general-purpose text and paste it in the comment text

However, since Quartus II does not support Japanese input, it is possible to use the above setting method, but basically we recommend using alphanumeric characters and underscores to create comments.