I have tried every single Mac translator app that is free or allows a free trial. This is the only acceptable one. It's not perfect, but it works for me. The keyboard shortcut works in Calibre reader, which is very important since the mac dictionary does not work in there, but I wish I didn't have to copy the text first. The shortcut should automatically translate the selected text in my opinion. I like the popup when selecting text in safari.
Problems: The sound does not work for russian. Also It does not translate offline; when my internet went out, this app was useless.