csv file with Unicode character like \U0082

How do you decode ? utf8 should do it. Unless your server encodes data incorrectly for instance as latin1 or latin2

This should keep the accented characters in the Codable struct MyStruct:

    func decodeData(jsonString: String) -> MyStruct? {
        
        let dataLues = jsonString.data(using: .utf8, allowLossyConversion: false) 
        let jsonDecoder = JSONDecoder()
        do {
            let decoded = try jsonDecoder.decode(MyStruct.self, from: dataLues!)
            return decoded
        } catch {
            print("Decode error", jsonString)
        }
        return nil
    }

the file is not a json, it's a csv (comma delimiter) from .dbf

I decode with

let data = try Data(contentsOf: URL(fileURLWithPath: path), options: NSData.ReadingOptions.mappedIfSafe)
      
let dataEncoded = String(data: data, encoding: .isoLatin1)

If I try to encode in utf8, dataEncoded is nil

after few search, in fact I do a loop over each character and check unicodescalar "String(char).unicodeScalars"

switch char1 {
      case "\u{0080}":
           charactere = "Ç"
      case "\u{0081}":
          charactere = "."
etc...

You could also use replacingOccurrences

myString = myString.replacingOccurrences(of: "\u{0080}", with: "Ç").replacingOccurrences(of: "\u{0081}", with: ".")

etc…