I remember using google translate in early GD.
I think this is your best bet at the moment: https://github.com/xinebf/google-translate-for-goldendict
Alternatively to described above Python script, there is pure Bash script for same purpose:
For Nix users:
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I think this is your best bet at the moment: https://github.com/xinebf/google-translate-for-goldendict