There is nothing wrong with having an indult-Tridentine nuptial Mass or a standard Roman-rite nuptial Mass said in Latin, although your priest may have difficulty obtaining an indult for the Tridentine if you and your fiance are not regular worshippers at an indult-Tridentine liturgy. The bishop is unlikely to grant such an indult purely to accommodate your chosen theme. Such permission by a bishop would likely be granted in order to allow a couple already deeply attached to the Tridentine liturgy to be married according to that rite. Your priest, though, may say the standard Roman-rite nuptial liturgy in Latin on his own initiative.
The problem with “theme” weddings is that the chosen “theme,” whatever it may be, tends to overpower the nuptial Mass and turn people’s attention to your cleverness and individual taste, rather than focus them on the sacraments that they should be witnessing and participating in (i.e., matrimony and the Eucharist). Theme weddings have become particularly popular in our society among those people who have already been living their lives as if they were married and thus are bored with the prospect of marriage. The “theme” allows them to dramatize their private fantasies while finally going through the ritual of marriage. Needless to say, such an attitude is hardly conducive to a successful marriage.
A wedding is not a popular play in which you dress up in costumes, set the stage, and perform. It is a sacred ritual – for Christians, the reception of a sacrament – that unites the couple and creates a new family. While weddings should certainly be festive, and may include personalized touches, the festivities and personal touches should be subordinate to the sacraments and should complement them rather than overpower them. If you want to include medieval touches to your wedding, go ahead; but please do not think of them as a “theme.” A good rule of thumb is that such touches should be so subtle that none of your guests will remark, “So, you decided on a medieval theme, huh?”