[imron]

Japanese writing is made up of a mix of 3 different scripts, kanji, hiragana and katakana.

The hiragana and katakana are syllabaries and don’t have the information density that you get with kanji.

I don’t imagine you’d get Japanese books that are more compact than their English counterparts because per sentence Japanese texts are comprised mostly of hiragana and katakana with a sprinkling of kanji.

Chinese on the other hand is all hanzi, and that does provide significant information density.

I used to have the lord of the rings in both English and Chinese on my bookshelf. The 3 volumes in Chinese where about the same thickness as a single volume in English (width and height were approximately the same) and this was with a much larger Chinese font required for legibility.