I've come up with the idea of perhaps making clones of pools but translated to spanish so as to make danbooru available to more people. But of course where this idea to be approved I would personally re-translate as many pools as I possibly can, as long as I don't have engagements in RL.
I would like to reiterate Soljashy's point from three years ago -- if, in the unlikely event that this is approved, then whoever doing the translation must be pretty damned sure to translate from the original Japanese instead of the English (or whatever language) notes. It doesn't matter how good your Spanish is or how good the English translator was, mistakes are bound to pop up when your play the telephone game with translations.
(It's okay if you do understand Japanese, even if it's a bit shaky, and you're only using the English notes as a reference. Still, if you're unsure, please look up a dictionary or ask other people for their opinion.)
Uploading duplicate images are a bad idea regardless. If you can't wait for the proposed UI changes to allow multiple languages (which may never come), your best options are to either hard-translate the images yourself and host it on your website/blog, or to set up a mirror booru service which caters to Spanish users.
(It's okay if you do understand Japanese, even if it's a bit shaky, and you're only using the English notes as a reference. Still, if you're unsure, please look up a dictionary or ask other people for their opinion.)
The only reason I don't do translation work here anymore is because I thought I wasn't supposed to translate unless I was sure I was right...
You should be confident that you read the words correctly and have translated them as correct as possible, yes.
Nobody's asking for perfect translations but if you're not confident that your translation was correct it's probably best to not bother. If you're pretty confident but not 100% behind it check_Translation exists but shouldn't be used as a crutch.