Some improvements to the wordcount plugin

1) allow for custom formatting of the output of the wordcount formatter
   This allows for formatting numbers correctly e.g. 1,042 in English
   locale and 1.042 in German locale.

2) cache values, so that no on every cursor move the wordcount needs to
   be recalculated.

autoload/airline/extensions/wordcount.vim

@@ -3,33 +3,17 @@
 
 let s:filetypes = get(g:, 'airline#extensions#wordcount#filetypes', '\vhelp|markdown|rst|org|text')
 let s:format = get(g:, 'airline#extensions#wordcount#format', '%d words')
+let s:formatter = get(g:, 'airline#extensions#wordcount#formatter', 'default')
 
-" adapted from http://stackoverflow.com/questions/114431/fast-word-count-function-in-vim
 function! s:update()
-  if &ft !~ s:filetypes
-    unlet! b:airline_wordcount
-    return
-  elseif exists("*wordcount")
-    let b:airline_wordcount = printf(s:format, wordcount()['words']).
-          \ g:airline_symbols.space . g:airline_right_alt_sep . g:airline_symbols.space
-  elseif mode() =~? 's'
-    " Bail on select mode
-    return
-  else
-    let old_status = v:statusmsg
-    let position = getpos(".")
-    exe "silent normal! g\<c-g>"
-    let stat = v:statusmsg
-    call setpos('.', position)
-    let v:statusmsg = old_status
-
-    let parts = split(stat)
-    if len(parts) > 11
-      let cnt = str2nr(split(stat)[11])
-      let spc = g:airline_symbols.space
-      let b:airline_wordcount = printf(s:format, cnt) . spc . g:airline_right_alt_sep . spc
-    else
-      unlet! b:airline_wordcount
+  if match(&ft, s:filetypes) > -1
+    if get(b:, 'airline_wordcount_cache', '') is# '' ||
+          \ b:airline_wordcount_cache isnot# get(b:, 'airline_wordcount', '') ||
+          \ get(b:, 'airline_change_tick', 0) != b:changedtick
+      " cache data
+      let b:airline_wordcount = airline#extensions#wordcount#formatters#{s:formatter}#format()
+      let b:airline_wordcount_cache = b:airline_wordcount
+      let b:airline_change_tick = b:changedtick
     endif
   endif
 endfunction
@@ -44,4 +28,3 @@ function! airline#extensions#wordcount#init(ext)
   call a:ext.add_statusline_func('airline#extensions#wordcount#apply')
   autocmd BufReadPost,CursorMoved,CursorMovedI * call s:update()
 endfunction
-

autoload/airline/extensions/wordcount/formatters/default.vim

@@ -0,0 +1,48 @@
+" MIT License. Copyright (c) 2013-2016 Bailey Ling.
+" vim: et ts=2 sts=2 sw=2
+
+function! airline#extensions#wordcount#formatters#default#format()
+  let words = string(s:wordcount())
+  if empty(words)
+    return
+  endif
+  let separator = s:get_decimal_group()
+  if words > 999 && !empty(separator)
+    " Format number according to locale, e.g. German: 1.245 or English: 1,245
+    let a = join(reverse(split(words, '.\zs')),'')
+    let a = substitute(a, '...', '&'.separator, 'g')
+    let words = join(reverse(split(a, '.\zs')),'')
+  endif
+  return  words . " words" . g:airline_symbols.space . g:airline_right_alt_sep . g:airline_symbols.space
+endfunction
+
+function! s:wordcount()
+  if exists("*wordcount")
+    return wordcount()['words']
+  else if mode() =~? 's'
+    return
+  else
+    let old_status = v:statusmsg
+    let position = getpos(".")
+    exe "silent normal! g\<c-g>"
+    let stat = v:statusmsg
+    call setpos('.', position)
+    let v:statusmsg = old_status
+
+    let parts = split(stat)
+    if len(parts) > 11
+      return str2nr(parts[11])
+    else
+      return
+    endif
+  endif
+endfunction
+
+function s:get_decimal_group()
+  if match(v:lang, '\v\cC|en') > -1
+    return ','
+  elseif match(v:lang, '\v\cde|dk|fr') > -1
+    return '.'
+  endif
+  return ''
+endfunction

doc/airline.txt

@@ -415,6 +415,20 @@ eclim <https://eclim.org>
   let g:airline#extensions#wordcount#filetypes = ...
   (default: markdown,rst,org,help,text)
 
+* defines the name of a formatter for word count will be displayed: >
+  " The default will try to guess LC_NUMERIC and format number accordingly
+  " e.g. 1,042 in English and 1.042 in German locale
+  let g:airline#extensions#wordcount#formatter = 'default'
+
+  " here is how you can define a 'foo' formatter:
+  " create a file in the dir autoload/airline/extensions/wordcount/formatters/
+  " called foo.vim
+  " this example needs at least Vim > 7.4.1042
+  function! airline#extensions#wordcount#formatters#foo#format()
+    return (wordcount()['words'] == 0 ? 'NONE' :
+        \ wordcount()['words'] > 100 ? 'okay' : 'not enough')
+  endfunction
+  let g:airline#extensions#wordline#formatter = 'foo'
 <
 -------------------------------------                   *airline-whitespace*
 * enable/disable detection of whitespace errors. >
@@ -507,9 +521,9 @@ exposed.
   let g:airline#extensions#tabline#formatter = 'default'
 
   " here is how you can define a 'foo' formatter:
-  " create a file in the dir autoload/airline/extensions/tabline/formatter/
+  " create a file in the dir autoload/airline/extensions/tabline/formatters/
   " called foo.vim
-  function! airline#extensions#tabline#formatter#foo#format(bufnr, buffers)
+  function! airline#extensions#tabline#formatters#foo#format(bufnr, buffers)
     return fnamemodify(bufname(a:bufnr), ':t')
   endfunction
   let g:airline#extensions#tabline#formatter = 'foo'