spell: Display spelling language

fixes: #1521

autoload/airline/init.vim

@@ -25,6 +25,7 @@ function! airline#init#bootstrap()
   call s:check_defined('g:airline_detect_paste', 1)
   call s:check_defined('g:airline_detect_crypt', 1)
   call s:check_defined('g:airline_detect_spell', 1)
+  call s:check_defined('g:airline_detect_spelllang', 1)
   call s:check_defined('g:airline_detect_iminsert', 0)
   call s:check_defined('g:airline_inactive_collapse', 1)
   call s:check_defined('g:airline_exclude_filenames', ['DebuggerWatch','DebuggerStack','DebuggerStatus'])

autoload/airline/parts.vim

@@ -65,7 +65,17 @@ function! airline#parts#paste()
 endfunction
 
 function! airline#parts#spell()
-  return g:airline_detect_spell && &spell ? g:airline_symbols.spell : ''
+  let spelllang = g:airline_detect_spelllang ? printf(" [%s]", toupper(substitute(&spelllang, ',', '/', 'g'))) : ''
+  if g:airline_detect_spell && &spell
+    if winwidth(0) >= 90
+      return g:airline_symbols.spell . spelllang
+    elseif winwidth(0) >= 70
+      return g:airline_symbols.spell
+    else
+      return split(g:airline_symbols.spell, '\zs')[0]
+    endif
+  endif
+  return ''
 endfunction
 
 function! airline#parts#iminsert()

doc/airline.txt

@@ -131,6 +131,10 @@ values):
 
 * enable spell detection >
   let g:airline_detect_spell=1
+
+* display spelling language when spell detection is enabled
+  (if enough space is available) >
+  let g:airline_detect_spelllang=1
 <
 * enable iminsert detection >
   let g:airline_detect_iminsert=0