It's not directly prohibited by the rules, since in theory you're targeting a different group of people and you're not doing it to gain visibility. I also don't recall reading any admin posts prohibiting or advising against it, so in theory, you shouldn't have any problems complying with Itch's quality guidelines.

However, there are many objections from a logical standpoint. Your game effectively becomes two separate games; that is, you have to make two updates, maintain two separate development logs on separate pages, and if someone leaves a positive comment or downloads your game in one language, it won't affect the statistics of the other page. This reduces your potential impact. For example, between Spanish and English, you might get 1,000 visits, which would allow you to appear on the first page. But by splitting the game, you now have 700 visits in English and 300 in Spanish. Therefore, neither of your versions will appear on the first page because you're dividing the visibility of the two projects.

/t/3946704/handling-multi-language-itchio-page

A few words.

Your game description is very short. You can just write both language versions on the same page. Also, this should work on a game page too, should you need to save space. /t/2151831/adding-spoiler-text-to-your-game-description

Tags are not translated. No one uses the tags you use. Only a handful games use  /games/tag-novela-visual , but 44000 use /games/genre-visual-novel

Itch is a English site. Spanish speakers that browse here will have ways to deal with that. Either they speak English or they use the translation feature of their browser or whatever. That means they will not use spanish tags. They know that no one uses those. And games can be sorted by having language features. Even if that feature seems kinda hidden.

Compare how the games in this list handle multi language game pages and try not to reinvent the wheel. The reach impact Hechelion describes will be substantial, if you split your visibility.

/games/lang-es