The technically correct and yet completely useless answer to your question is that, since the language code used is ES, the expected dialect is some hypothetical universal Spanish.
It’s referred to one of the current discussion topics as (oficial), so I think the intent is RAE Spanish. Am I interpreting that parenthetical correctly @SidV?
In the past we had separate translations for Latin American, Mexican, and Argentine dialects, but it looks like those did not carryover from Transifex 
CrowdIn. Presumably there wasn’t enough actually translated to keep them around.
If someone were to follow the procedure we could add one back in. That page says those “instructions are currently out of date”, so we’ll have to petition someone – likely @gerhard – to update it.