Hallo!

You should certainly begin with Jorge Luis Borges. He's been translated to Deutsch, and has actually gotten fairly popular in Germany in this last few years. Borges is absolutely amazing, but didn't get that much international distribution in his time mostly because of political issues (he certainly deserved a Nobel, that he was never given). He was a native Spanish speaker, but also spoke English almost natively (his grandma's native language). He was very interested in Saxon languages, and studied ancient Saxon languages, English and Deutsch. He was fascinated with your language, and he did a lot of translations of German texts to Spanish, including Heine and Kafka. He even wrote several Poems dedicated to the Deutsch language and German writes, such as Al Idioma Aleman (here is an English translation), and A un poeta Sajon.

Read everything and anything by him you can get your hands on, it's absolutely delightful. Maybe start with The Aleph, The Garden of Forking Paths, Funes the Memorious, or The Other.

You should also read some by Roberto Arlt and Julio Cortazar. Very different styles, both of them absolutely amazing. Start with The Seven Madmen by Arlt, if you like it (you will), then read The Flamethrowers. With Cortazar, start with All Fires The Fire (short stories), specially Southern Highway and All The Fires the Fire. If you want a Novel, go with Rayuela.

You will also enjoy Horacio Quiroga (Originally from Uruguay, but he lived extensively in Argentina, and his best stories where written in Misiones province). Magic-realism, with a twist. Jungle settings, man vs nature, absolutely fantastic.