How to get Vim to highlight non-ascii characters?

Question

I\'m trying to get Vim to highlight non-ASCII characters. Is there an available setting, regex search pattern, or plugin to do so?

Answer 1

Based on the other answers on this topic and the answer I got here I've added this to my .vimrc, so that I can control the non-ascii highlighting by typing 1. It also shows inside comments, although you will need to add the comment group for each file syntax you will use. That is, if you will edit a zsh file, you will need to add zshComment to the line

au BufReadPost * syntax match nonascii "[^\x00-\x7F]" containedin=cComment,vimLineComment,pythonComment

otherwise it won't show the non-ascii character (you can also set containedin=ALL if you want to be sure to show non-ascii characters in all groups). To check how the comment is called on a different file type, open a file of the desired type and enter :sy on vim, then search on the syntax items for the comment.

function HighlightNonAsciiOff()
  echom "Setting non-ascii highlight off"
  syn clear nonascii
  let g:is_non_ascii_on=0
  augroup HighlightUnicode
  autocmd!
  augroup end
endfunction

function HighlightNonAsciiOn()
  echom "Setting non-ascii highlight on"
  augroup HighlightUnicode
  autocmd!
  autocmd ColorScheme *
        \ syntax match nonascii "[^\x00-\x7F]" containedin=cComment,vimLineComment,pythonComment |
        \ highlight nonascii cterm=underline ctermfg=red ctermbg=none term=underline
  augroup end
  silent doautocmd HighlightUnicode ColorScheme
  let g:is_non_ascii_on=1
endfunction

function ToggleHighlightNonascii()
  if g:is_non_ascii_on == 1
    call HighlightNonAsciiOff()
  else
    call HighlightNonAsciiOn()
  endif
endfunction

silent! call HighlightNonAsciiOn()
nnoremap 1 :call ToggleHighlightNonascii()