This code determines the buffer language by counting several small and often used words characteristic each language and ranks them. The original version was posted by JeanPhilippeTheberge on See GuessLang and AutoLangMode for an alternative.

I use this code to set the WikiLanguage for my wiki pages. I modified it in order to be non-interactive, and I probably messed with the regexps a bit. This is the version by JeanPhilippeTheberge, modified by AlexSchroeder. For the original, see Groups:Guessing+a+language.

    (defvar guess-language-rules
      '(("en" . "\\<\\(of\\|the\\|and\\|or\\|how\\)\\>")
        ("de" . "\\<\\(und\\|oder\\|der\\|die\\|das\\|wie\\)\\>") 
        ("fr" . "\\<\\(et\\|ou\\|[ld]es\\|que\\)\\>")
        ("pt" . "\\<\\(de\\|para\\|e\\|ou\\|como\\)\\>"))
      "Alist of rules to determine the language of some text.
    Each rule has the form (CODE . REGEXP) where CODE is a string to
    identify the language (probably according to ISO 639), and REGEXP is a
    regexp that matches some very common words particular to that language.
    The default language should be listed first.  That will be the language
    returned when no REGEXP matches, as would happen for an empty

    (defun guess-buffer-language ()
      "Guess language in the current buffer."
        (goto-char (point-min))
        (let ((count (map 'list (lambda (x)
                                  (cons (string-to-number
                                         (count-matches (cdr x))) (car x)))
          (cdr (assoc (car (sort (map 'list 'car count) '>)) 

Here is an interactive wrapper:

    (defun guess-language ()
      "Guess language in the current buffer."
      (message (guess-buffer-language)))

On my Emacs22 count-matches returns integer so string-to-number triggers error. Just replace (cons (string-to-number (count-matches (cdr x))) (car x))) with (cons (count-matches (cdr x)) (car x)))

If the above code does not work for you reliably, or if you need some other languages which are not covered, you can use an external tool called “mguesser”. Here’s a code snippet for this:

(setq guess-buffer-default "en")
(defun guess-buffer-language ()
  "Guess language using mguesser."
  (let ((buf (get-buffer-create " *mguesser*"))
    (with-current-buffer buf
    (setq proc
          (start-process "mguesser" buf "/usr/bin/mguesser"))
    (process-send-region proc (point-min) (point-max))
    (process-send-eof proc)
    (accept-process-output proc 0.3)
    (delete-process proc)
    (with-current-buffer buf
      (goto-char (point-min))
          (if (looking-at "^[0-9.]+\\s-+\\([a-z-]+\\)")
              (match-string 1)