Please check our article on how to translate Jupiter and note that you have to use the .po .mo file that comes with files of jupiter you have downloaded. You are free to translate only the words that you need and you can leave others not translated. If you use BBpress or Woocommerce for full translation you have to translate the plugins too as not all words are overridden in Jupiter translation files and some come directly from the plugins. Please click here to read the article.