I like the site having tags in Spanish, but my eyes bleed when I see all accents are missing (and I imagine that diéresis also). Can tags written in Spanish be written as they should (with accents)?
No, accents and diacratic marks are stripped from tags on the SE network.
If you want this changed, I suggest posting a feature request on MSO. I suspect it won't be done, but it wouldn't hurt to ask.