Well, for reliable mature manhwa sites, you could try Manhwa Zone or Mature Manhwa World. These sites update regularly and have a good selection of titles. But be aware of the age restrictions and follow the site's rules.
One of the notable Spanish manhwa sites is MangaGo.es. It provides a user-friendly interface and a good selection of manhwa. Additionally, ManhwaFever.es is worth checking out as it has a diverse range of genres and frequently adds new series.
You should avoid looking for manhwa scan sites. They violate copyright laws and aren't good for the development of the manhwa industry. Instead, check out official platforms where you can enjoy manhwa legally and with better quality.
You could try ManhwaArab. This site provides not only a good selection of Arabic manhwa but also features community sections where you can interact with other fans and discuss your favorite titles.