Moderator note: this should be fixed in Stardew Valley 1.6.9.
Forwarded report from a Discord user:
ES Special Item & Powers
Should be special items (plural) & powers, currently translated as "Objeto Especial y Poderes" (probably leftover from when English was translated that way). Probably should be something like Objetos Especiales y Poderes
File is Strings/1_6_Strings.es-ES.xnb
All translation issues reported up to this point should be fixed in the upcoming Stardew Valley 1.6.9. Feel free to report any issues which still happen when you get the update. Thanks for reporting them (and thanks to the Spanish translator for fixing them)!
"Mystery boxes can now be found" has a weird translation, something like "Cajas misteriosas pueden ser encontradas ahora". Maybe a better translation could be "Ahora se pueden encontrar Cajas Misteriosas"