1)
Quickly searching for image dupes is technically complicated. I would very much like to add it, but it will take me time. Prioritising this is up for vote now, if you are interested, here:
https://poal.me/4bhdd6
2)
I am not sure what you mean by translating tags–is there a particular set of tags you see on pixiv that you would like to appear how they are on danbooru? Or do you mean literal translation from Japanese to English? In any case, Tag siblings usually do these sorts of tasks. You can read more about them here:
http://hydrusnetwork.github.io/hydrus/help/advanced_siblings.html
Although the manage siblings dialog is a bit creaky and overloaded now and could do with updating. That's also up for vote right now!