Created attachment 93622 [details] Interface bug An image says more than thousand words. On the left, the Japanese interface on a French Windows 7 (default language for non-Unicode applications: Japanese). On the right, the Japanese interface on a Japanese Windows 8.1 The first is badly screwed up: about half of the words are replaced by squares. Unusable. The second one is perfect.
The attachment is a gif image. It does not show up correctly, at least on my PC - I do not know why!
The image loads fine here FWIW. Based on it, it seems that LibreOffice is not falling back to a font containing all of the missing Japanese characters, that is why you are seeing squares. HAve you tried resetting your user profile? See http://wiki.documentfoundation.org/UserProfile
If you look carefully at the image, you'll see that the Kanji (Chinese characters) are correctly shown, while Katakana is replaced by squares. This may perhaps give the developers some hint? I guess you'll need to get in touch with the Japanese team to fix this bug.
Resetting user profile does not help at all - same result, Kanji shown, Katakana lost.
*** This bug has been marked as a duplicate of bug 45996 ***