a wedding in two languages

I have been to a couple of weddings where the couple have each said their vows in the other person's language, so it should be feasible to even do this if you wanted to (from memory, I think the witnesses do have to understand what is being said, but you could always check this) They also had readings in both languages, and either included a translation in the order of service or gave a brief explanation.

Regarding invitations and menus etc, the important thing is to check how many of your guests are fluent in the language you are using. If you have some guests who are only fluent in Spanish and others who are only fluent in English, then you really need to make sure that the basics are in both. If everyone is fluent in the same language, then you can use that for all the important stuff, and include some of the less well spoken language where being able to understand is less important - because it doesn't really matter if your guests don't fully understand the poem you picked for the ceremony, but if they don't understand where the wedding is or what time it starts...