Created attachment 178963 [details]
This is the screen capture of the application showing a mixture of languages

SUMMARY

In both Japanese and Chinese, there are overlapping but not the same unicode range for the Kanji (Chinese Characters).
In KDiff3, the texts in the buttons, tooltip, etc are showing incorrect Kanji.
For Japanese users, the Kanji shall be Japanese Kanji not Simplified Chinese Characters. 
I have changed the fonts to Japanese fonts but in vain as some Chinese Characters are with distinct unicodes.
Example: (Japanese) 移動 <-> (Simplified Chinese) 移动


STEPS TO REPRODUCE
1.  Install and Setup KDiff3 with the following settings.
Configuration Language - KDiff3
Primary Language: 日本語 (ja)
Fallback Language: 日本語 (ja)
Fallback Language: 日本語 (ja)
Fallback Language: 中国語 簡体字 (zh_CN)
2. Restart the application to refresh the language settings.

OBSERVED RESULT
Some Simplified Chinese characters are shown in the toolbar. like "移动", "合并"
(Some terms are not just kanji issue. I think the translation is incomplete so this become fallback lang)

EXPECTED RESULT
No Simplified Chinese characters are shown in the toolbar. The text should be displayed as "移動" ,"マージ"

SOFTWARE/OS VERSIONS
Windows: 10

ADDITIONAL INFORMATION
I need to work with files including Simplified Chinese characters. So I have to set the fallback. That is primary lang is Japanese and secondary lang is Simplified Chinese.
(Some terms are not just kanji issue. I think the translation is incomplete so this become fallback lang)