The announcement of Pokémon Scarlet and Violet came with a trailer that showed off the region it's set in, and it looks as though it could be modeled on Spain. No official confirmation has come from Game Freak as of yet, and neither has the name of the region, but it's so far become accepted by much of the fanbase. Considering the evidence available, it seems probable that Scarlet and Violet will be set in a fictional version of Spain - unless a major curveball is thrown between now and the game's launch.
Pokémon Scarlet and Violet's region was shown during the Pokémon Presents February 2022 video. It promised an open-world region without any transitions between areas, which is exciting for those who were hoping for the same thing in the time leading up to Pokémon Legends: Arceus' release. If Pokémon Scarlet and Violet is like Legends: Arceus, then it would appear that the series has a promising future in terms of innovation, and is hopefully listening to its players. No other details about the region were given aside from these facts, not even the name, so many are working overtime to try and get any scrap of information they can out of the trailer.
The reason many believe the next games' region to be based on Spain is due to some prominent landmarks shown in the trailer, which bear a close resemblance to real-life ones in the real-life country. The names and appearances of two of the starters also hold a clue, although it may be less obvious. What this means for the games and the region itself can't be said for certain at the moment, but many have their own theories. The Pokémon revealed in Scarlet and Violet's trailer, aside from the starters, don't offer many hints, but more may come as time goes on.
Evidence For Pokémon Scarlet & Violet's Region Being Based On Spain
The primary reason that many believe Pokémon's newest region to be based on Spain is that many of the buildings and structures bear a striking resemblance to ones in real life. The large church-like building with the Poké Ball on top, for example, is very similar to famous Spanish churches, quite possibly La Sagrada Famìlia in Barcelona specifically. The windmills from Pokémon Scarlet and Violet's trailer also appear to be based on the Consuegra windmills in the Spanish mountains. Lastly, the colorful town square shown when Pikachu is introduced seems to be a reference to the Placa de Cataluña, also in Barcelona.
There are also the names and appearances of the starter Pokémon. Sprigatito, the Grass-type that's already become wildly popular, contains the Spanish word for a cat - or a "little cat" specifically - "Gatito". Everything about Scarlet and Violet's starter Pokémon is still mostly unknown, but they have provided evidence to suggest the inspirations behind the game's region. Fuecoco also looks somewhat like a chili pepper, which makes sense since it's a Fire-type. However, its white face means that it looks like a stuffed piquillo pepper, a Northern Spanish dish often made with cream cheese, meat, or seafood, in particular. Its name also appears to be a combination of "fuego" and "cocodrilo", the words for fire and crocodile respectively. Quaxly doesn't appear to offer much of a hint, but some may be seeing things that most don't.
What a Pokémon region based on Spain means for Scarlet and Violet, and the series as a whole, is unknown. It's possible that other Spanish influences will come with the games, like how past ones showed the countries that their regions were based on, as was the case with Pokémon Sword and Shield and its UK setting. Pokémon Scarlet and Violet's setting is yet to be confirmed, but evidence that it will be set in Spain is fairly convincing.