Finding non-ASCII characters

Sourced from Stackoverflow.com (https://stackoverflow.com/questions/2124010/grep-regex-to-match-non-ascii-characters) thanks to Alix Axel
This will match a single non-ASCII character:

[^\x00-\x7F]

This is a valid PCRE (Perl-Compatible Regular Expression).

You can also use the POSIX shorthands:

[[:ascii:]] - matches a single ASCII char
[^[:ascii:]] - matches a single non-ASCII char

For Libre Calc or Libre Write do a Find & Replace (Ctrl + H) to get this menu: