This has definitely been an issue over time, and actually moreso (as far as we've heard) for Spanish than for any other language. There is a custom locale plugin (see System Plugins -> Generic Plugins -> Custom Locale) which allows you to customize any installed locale on your system. I think that this is a short-term solution though (or one better suited for special cases), because it only standardizes one install.
Another alternative would be to have one institution take over responsibility for Spanish; do an audit; and standardize it as well as possible. We've had this happen with French, but only because we're in Canada (so French important) and because we have a reciprocal partnership with a French university. We unfortunately don't have the money to put towards maintaining a Spanish translation, and we've seen many, many people and institutions work on Spanish in particular, which contributes to the lack of standardized terminology.
Another recent suggestion to develop a basic standards list/grammar/ruleset for Spanish translators (and the same kind of thing for other translators). While we can't contribute directly to the discussion and creation of such a list, we're happy having people use our wiki to do just that. As a matter of fact, there's even a page right here
, under the Languages subheading, for just such a thing for Spanish.
Other suggestions are very welcome. If you'd like more information on working with translations, just let us know!