A small Lisp program which uses Google Translation API

(Diary of an Old AI Researcher who is still Programming)

2 August 2025

I've been enjoying using Duolingo to learn French, German, and Italian. I often rely on Google Translate to check how certain expressions are rendered in those languages. However, it can get a bit tedious to repeatedly translate the same English sentence into French, German, and Italian one by one. So, I decided to write a program that uses the Google Translate API to automatically generate translations of an English expression into all three languages. This time, I chose to write the program in Common Lisp. I’ve grown a little bored with Python lately, and as an old researcher, I used to write a lot of Lisp code back in the day. I wanted to revisit those good old times. At first, I tried using modern AI tools to help generate the code. Unfortunately, the programs they produced didn’t work as expected. I found several critical errors and had to fix them manually. Here’s the corrected Lisp program:

; You should get a Google Cloud API Key from https://cloud.google.com/translate
; In your .bashrc add
; export GOOGLE_API_KEY="YOUR API KEY"

(ql:quickload '(:drakma :cl-json :babel))

(defpackage :google-translate
  (:use :cl :drakma :cl-json)
  (:export :translate))

(in-package :google-translate)

(defun get-api-key ()
  (or (uiop:getenv "GOOGLE_API_KEY")
      (error "GOOGLE_API_KEY not found")))


(defun translate-with-google (text source target)
  "Translate TEXT from SOURCE language to TARGET language using Google Translate API."
  (let* ((url "https://translation.googleapis.com/language/translate/v2")
	 (api-key (get-api-key))
         (params `(("q" . ,text)
                   ("source" . ,source)
                   ("target" . ,target)
                   ("format" . "text")
                   ("key" . ,api-key)))
         (response (drakma:http-request url :method :post
                                            :content-type "application/x-www-form-urlencoded"
                                            :parameters params))
	 (response-string (babel:octets-to-string response :encoding :utf-8))
	 (json (cl-json:decode-json-from-string response-string)))
    (cdr (assoc  :translated-text (cadr (assoc :translations (cdr (assoc :data json))))))))

(defun translate (phrase)
  (format t "French:~%~a~%~%" (translate-with-google phrase "en" "fr"))
  (format t "German:~%~a~%~%" (translate-with-google phrase "en" "de"))
  (format t "Italian:~%~a~%~%" (translate-with-google phrase "en" "it")))

;; usage:
;(use-package :google-translate)
;(translate "Hello, world!")
            

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