I don't know of any qualification required. If you think the existing translations are poor, and want to try to improve on them, or translate some texts that are not available in Spanish, then do it.
If you're translating from English there's a double problem, because existing translations from Pali may also be wrong. Ideally, you should learn Pali and translate directly from the Pali.
If you do a thorough scholarly job, with footnotes to explain the reasons for your choices, and references to the Pali texts and Commentaries like Bhikkhu Bodhi and Maurice Walshe have done in their Wisdom Publications, then readers will be able to check your work for accuracy.
In the forward, explain your academic qualifications (or acknowledge the lack thereof). Everyone is responsible for their own actions — however good a translation is, some are able to misinterpret it, and however bad it is, some are able to see through the translator's errors.
Even if your work turns out to be nearly useless to others, at least you will learn something in the process of making the translation.