(There are Japanese characters assigned to unicode code points. But also there can be fonts assigning Japanese glyphs to code points officially used for other purposes. That’s technical e.g. Software is a technical thing.)
I don’t know anything about Japanese. Just looked around a bit.
Japanese is written in Hiragana and/or Katakana chartacters. Unicode has assigned code points in the range o U+3000 to U+31FF to these characters. If “Japanese text” is exclusively written with these characters, you can find it in principle with the help of a regular expression (RegEx). To construct an actually working search expression accepting exactly non-empty sequences of the mentioned characters, shaped as usable in LibO will again require as well some knowledge about writing in Japanese as about technical aspects of the unicode system. The “first idea” [\u3000-\u31FF]+ doesn’t work as expected. In Calc anyhow such an expression will find the cells containing a match. You can(?) use
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]
as a Regex, but it doesn’t look like a final solution. Try a web-search for “regular expression for japanese characters”.
To first mix up text pieces in two languages inside single cells and then to expect them to be separately treatable by the software is somehow bold. You may find a solution to separate English from Japanese thinking the technical way, and I may try to help you again with it when I find time. Alas! It’s completely useless if you just want to base an even worse mistake on it: Using different fonts inside of single cells as a rule instead of as a rare exception.
