Install LanguageTool version 3.0 or later (and java) https://languagetool.org/

Put this file into load-path'ed directory, and byte compile it if desired. And put the following expression into your ~/.emacs.

(setq langtool-language-tool-jar "/path/to/languagetool-commandline.jar")
(require 'langtool)

Alternatively, you can set the classpath where LanguageTool's jars reside:

(setq langtool-java-classpath
      "/usr/share/languagetool:/usr/share/java/languagetool/*")
(require 'langtool)

You can use HTTP server implementation which is now testing. This is very fast, but has security risk if there is multiple user on a same host. You can set both of langtool-language-tool-jar and langtool-language-tool-server-jar the later is prior than the former. [Recommended] You should set langtool-language-tool-jar correctly full of completion support like available languages.

(setq langtool-language-tool-server-jar "/path/to/languagetool-server.jar")

You can change HTTP server port number like following.

(setq langtool-server-user-arguments '("-p" "8082"))

These settings are optional:

• Key binding if you desired.

(global-set-key "\C-x4w" 'langtool-check)
(global-set-key "\C-x4W" 'langtool-check-done)
(global-set-key "\C-x4l" 'langtool-switch-default-language)
(global-set-key "\C-x44" 'langtool-show-message-at-point)
(global-set-key "\C-x4c" 'langtool-correct-buffer)

• Default language is detected by LanguageTool automatically. Please set langtool-default-language if you need specific language.

(setq langtool-default-language "en-US")

Otherwise, invoke M-x langtool-check with C-u (universal-argument)

• Currently GNU java version is not working. Please change the variable to your favorite java executable.

(setq langtool-java-bin "/path/to/java")

• Maybe your LanguageTool have launcher. (e.g. Gentoo) You need to set langtool-bin. See mhayashi1120#24

(setq langtool-bin "/usr/bin/languagetool")

• Maybe you want to specify your mother tongue.

(setq langtool-mother-tongue "en")

• To customize LanguageTool commandline arguments.

(setq langtool-java-user-arguments '("-Dfile.encoding=UTF-8"))

You can also make the variable to buffer local like following:

(add-hook '**SOME**-mode-hook
          (lambda () (set (make-local-variable 'langtool-java-user-arguments)
                         '("-Dfile.encoding=UTF-8"))))

NOTE: Although there is no good example, langtool-user-arguments is a similar custom variable.

• To check current buffer and show warnings.

M-x langtool-check

Check with different language. You can complete supported language with C-i/TAB

C-u M-x langtool-check

• To correct marker follow LanguageTool suggestions.

M-x langtool-correct-buffer

• Go to warning point you can see a report from LanguageTool. Otherwise:

M-x langtool-show-message-at-point

• Show LanguageTool report automatically by popup This idea come from: http://d.hatena.ne.jp/LaclefYoshi/20150912/langtool_popup

(defun langtool-autoshow-detail-popup (overlays)
  (when (require 'popup nil t)
    ;; Do not interrupt current popup
    (unless (or popup-instances
                ;; suppress popup after type `C-g` .
                (memq last-command '(keyboard-quit)))
      (let ((msg (langtool-details-error-message overlays)))
        (popup-tip msg)))))

(setq langtool-autoshow-message-function
      'langtool-autoshow-detail-popup)

• To finish checking. All langtool marker is removed.

M-x langtool-check-done