Make hunspell work with emacs and german language

To check if the dictionary is listed in the path run hunspell -D. It should output something along those lines:

...
/usr/share/hunspell/en_US
/usr/share/hunspell/de_BE
/usr/share/hunspell/de_LU
/usr/share/hunspell/de_DE
...

Next, add your preferred dictionaries to ispell-local-dictionary-alist in your .emacs file

(add-to-list 'ispell-local-dictionary-alist '("deutsch-hunspell"
                                              "[[:alpha:]]"
                                              "[^[:alpha:]]"
                                              "[']"
                                              t
                                              ("-d" "de_DE"); Dictionary file name
                                              nil
                                              iso-8859-1))

(add-to-list 'ispell-local-dictionary-alist '("english-hunspell"
                                              "[[:alpha:]]"
                                              "[^[:alpha:]]"
                                              "[']"
                                              t
                                              ("-d" "en_US")
                                              nil
                                              iso-8859-1))

(setq ispell-program-name "hunspell"          ; Use hunspell to correct mistakes
      ispell-dictionary   "deutsch-hunspell") ; Default dictionary to use

In addition to that you can define a function to switch between the german and english dictionaries and bind it to C-c d for example

(defun switch-dictionary-de-en ()
  "Switch german and english dictionaries."
  (interactive)
  (let* ((dict ispell-current-dictionary)
         (new (if (string= dict "deutsch-hunspell") "english-hunspell"
                   "deutsch-hunspell")))
    (ispell-change-dictionary new)
    (message "Switched dictionary from %s to %s" dict new)))

(global-set-key (kbd "C-c d") 'switch-dictionary-de-en)