They both require translate-shell… Light Dict did not worked for me, too. Translate Indicator works, but I can not paste text, only type it, that is not cool, otherwise that extension would be good.
I use Dialect app, which is ‘integrated’ to gnome search. ‘’ because integration does not mean text is autotranslated, you need to click dialect and the app opens with search query. But it works and works better, than those extensions.