Oversetter is a simple translation app, which allows you to translate content directly from your menubar. It is open-source application based on Angular and Electron. It uses free API of Yandex Translate for text translation. That means you need to register a free API key to use the program.
InstantTranslate makes it really easy to translate a selection of text in the application you are working in from one language to another language.
One World Dictionary by Ascendo is a leading multilingual reference tool for Apple desktops.
