You can achieve what you want using Rule-Based Labeling, but you need to separate the Japanese labels and English Labels into two fields. Rule-Based Labeling option enables you to add labels from different fields and customize them as you like by changing font name, color, size and use offset to place them above each other as you can see below:
To do this:
- Go to
Layer properties -> Labels
- Define the fields that you want to use in the labeling, each one separately. In this example, I used Name_JP and Name_EN.
- Use the style for each one independently and customize each one as you like.
- The most important is to use
Placement for the one of the labels so that they can be above each other. For the first label field I used the following placement settings:
For the second label field I used the following settings:
Tested on QGIS 3.0.1, But it can also applied in QGIS 2.18 because Rule-Based Labeling option is available.