Strange values on Serial Monitor even with matched baud rate
You can't concatenate string and value inside Serial.println().

Print them using two different Serial.println().

int pin12;
int A12 = A12;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  pin12 = analogRead(A11);

  Serial.print("pin 12 is ");
  Serial.println(pin12);

  delay(5000);
}