Question: I can't have any acid in my diet, so I need a good substitute for it for my dishes. Like lemon, orange, citric acids and vinegar. Thank you

Answer: 
If you search for a non-acid substitute for souring the food / raising the tartness: There is no substitute. The sensation of a tart dish is caused by lowering the pH at the corresponding taste buds. [By definition](https://en.wikipedia.org/wiki/Taste#Sourness) tasting sourness is detecting an acid.
Another reason you can't replace acids is that they are involved in important *chemical* reactions. Some flavors are soluble acid but not in just water, and also acid helps deglaze pans because it's a stronger solvent than water alone.