config.py

YandexApiKey = 'Your.Yandex.Translate.API.Key.Should.Be.Here'

main.py

#!/usr/bin/python

import config
import sys
import requests
import json
import urllib


def error(message, status_code):
    sys.stderr.write(message + '\n')
    sys.stderr.write('Status code: {0}\n'.format(status_code))


textFromInput = ''.join(sys.stdin.readlines())

urlDetectLanguage = 'https://translate.yandex.net/api/v1.5/tr.json/detect?key={0}&text={1}'
urlTranslate = 'https://translate.yandex.net/api/v1.5/tr.json/translate?key={0}&lang={1}&text={2}'

requestDetectLanguage = requests.post(urlDetectLanguage.format(config.YandexApiKey, urllib.quote(textFromInput)))

if requestDetectLanguage.status_code == 200:
    detectedLanguage = json.loads(requestDetectLanguage.text)['lang']
    langPair = ''

    if detectedLanguage == 'ru':
        langPair = 'ru-en'
    else:
        langPair = detectedLanguage + '-ru'

    requestTranslate = requests.post(urlTranslate.format(config.YandexApiKey, langPair, urllib.quote(textFromInput)))

    if requestTranslate.status_code == 200:
        translatedText = ''.join(json.loads(requestTranslate.text)['text'])
        sys.stdout.write(translatedText.encode('utf-8'))
    else:
        error('Error with translating', requestTranslate.status_code)
else:
    error('Error with language detect', requestDetectLanguage.status_code)

translate.sh

#!/usr/bin/env bash

TEXT=$(xsel -o)

TRANSLATED=`echo $TEXT | python /path/to/previous/script/main.py`

notify-send "$TEXT" "$TRANSLATED" -i accessories-dictionary -t 2000

echo $TRANSLATED | xsel --clipboard