Season the two halves of tongue with salt and allow to sit in the fridge on a plate for 2 hours or overnight.
Prior to cooking, remove from fridge and allow to rest at room temperature for 30 minutes.
Heat butter in a medium soup pot or small Dutch oven until melted.
Add onion and cook on medium heat for 5 minutes.
Add the salted beef tongue, chicken stock, soy sauce, coca cola, water, cinnamon sticks, bay leaves, cloves, peppercorns, oregano, red pepper flakes, smoked paprika, and freshly-ground black pepper.
Bring to just below a simmer and cook slowly for 2 hours, stirring occasionally.
After two hours of cooking, remove the beef tongues from the liquid and carefully cut off all the papillae and exterior layer of skin on the tongue, reserving the flesh.
Cut the tongue meat into 1.5” cubes and place back into the braising liquid.
Continue to cook for an additional 5-6 hours.
During the last two hours of cooking, add the rice wine vinegar and adjust saltiness of the broth to taste.
While the beef tongue is cooking, prepare the additional taco components.
Combine the red onion, lime zest, lime juice, red pepper flakes, fresh pineapple, fresh jalapeno, and cilantro stems and stir to combine.
Taste pickled mixture and adjust seasoning with salt and freshly-ground black pepper.
Allow pickled mixture to sit in the fridge while the tongue continues cooking and you prepare the remaining taco components.
Finely slice the purple cabbage and set aside.
When the beef tongue is finished cooking and is tender, turn off the heat and allow the meat to cool in the braising liquid.
Put in the fridge if using on another day.
If preparing the tacos immediately, slice the tongue meat into 1/8” slices and set aside.
Warm tortillas in the oven at 300F, wrapped in aluminum foil.
Warm slices of beef tongue in a small sauce pot with a small amount of the braising liquid to preserve moisture in the beef.
Construct tortillas with sour cream, beef tongue, pickled vegetables and pineapple, purple cabbage, fresh cilantro, and freshly-cut wedges of lime.