Unity 5 Control via wasd with rotation - unity3d

Question

I try to implement a simple controlling for my camera in Unity. Successfully I react on pressed w, a, s, d and move the camera. I also want to implement a rotation (Later on rotation with mouse, but at first a rotation using the keys e and q). I've written this script to update my camera but the problem: If you turn around, the update process for my keys w, a, s and d are not working correctly. F.e. I want to go left, but I'll go right. I have no idea how to solve this problem. Can someone give me an idea?
Here is my source code. Hope you'll understand what's my problem.
float translation_v = -(Input.GetAxis ("Vertical")) * 4.0F * Time.deltaTime;
camera.transform.position += new Vector3 (0, 0, translation_v);
float translation_h = -(Input.GetAxis ("Horizontal")) * 4.0F * Time.deltaTime;
camera.transform.position += new Vector3 (translation_h, 0, 0);
float rotation = -(Input.GetAxis ("Rotate_Player")) * 4.0F * Time.deltaTime * 10F;
camera.transform.Rotate(new Vector3(0F, rotation, 0F));
Vector3 pos = camera.transform.position;
pos.y = terrain.GetComponent<Terrain>().SampleHeight(camera.transform.position)+1;
camera.transform.position = pos;

Answer 1

First, Unity has standard components for first person controller and you don't have to do it from scratch, check out Assets -> Import Package -> Characters.
Assuming you do it for educational purposes and just want to implement it yourself: as far as I understood you want to move in the direction of the camera. So, what you need is to multiply the value you add to camera.transform.position by current camera rotation, i.e instead of
camera.transform.position += new Vector3 (0, 0, translation_v);
use
camera.transform.position += (camera.transform.rotation * new Vector3 (0, 0, translation_v));
and same for horizontal. You may also consider moving rotation update before position update. The final code would look like this:
float rotation = -(Input.GetAxis ("Rotate_Player")) * 4.0F * Time.deltaTime * 10F;
camera.transform.Rotate(new Vector3(0F, rotation, 0F));
float translation_v = -(Input.GetAxis ("Vertical")) * 4.0F * Time.deltaTime;
camera.transform.position += (camera.transform.rotation * new Vector3 (0, 0, translation_v));
float translation_h = -(Input.GetAxis ("Horizontal")) * 4.0F * Time.deltaTime;
camera.transform.position += (camera.transform.rotation * new Vector3 (translation_h, 0, 0));
Vector3 pos = camera.transform.position;
pos.y = terrain.GetComponent<Terrain>().SampleHeight(camera.transform.position)+1;
camera.transform.position = pos;