I\'m writting a simple paragraph in both English and Japanese, using only HTML and CSS. The English text breaks lines normally (when a word doesn\'t fit on a line anymore, i
English separates words with spaces, Japanese doesn't.
Whether characters in Japanese form a word or not depends on context. In many cases, looking for certain grammatical (Kana) particles could be used to separate words - but this wouldn't even be close to being reliable.
Essentially, you'd need a Japanese dictionary / understanding of the language to identify where the words start and end - a browser won't know how to do this.
Alternatively, if you know the start and end of the words, you could perhaps wrap each one in a span - then use CSS to ensure each span wraps to a new line as a whole when it doesn't fit.