onClickListener does not work in fragment

I think problem is here in your code

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{ 
.....
....
 //problem is here below line
 return inflater.inflate(R.layout.input_fgmt, container, false);
}

return your already inflated view

 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    { 
        View inputFragmentView = inflater.inflate(R.layout.input_fgmt, container, false);
    .....
    ....

     return inputFragmentView;
    }

change

 return inflater.inflate(R.layout.input_fgmt, container, false);

to

 return InputFragmentView ;

Also change with this:

translate_button.setOnClickListener(new View.OnClickListener()
{
    @Override
    public void onClick(View view)
    {
        Log.d("Test", "onClickListener ist gestartet");
        Toast.makeText(getActivity().getApplicationContext(), "Test", Toast.LENGTH_LONG).show();
        saveInString();

    }
});

and import as a import android.view.View;

Do this changes to your code

1. on class definition:

    public class InputFragment extends Fragment implements View.OnClickListener
   

2. on calling setOnClickListener:

       translate_button.setOnClickListener(new View.OnClickListener()
       {
             @Override
             public void onClick(View InputFragmentView)
             {
                     Log.d("Test", "onClickListener ist gestartet");
                     Toast.makeText(getActivity().getApplicationContext(), "Test", Toast.LENGTH_LONG).show();                                    
                     saveInString();
             }
        });
   

The best way to get all views created you should to redefinition the methode :

@Override
public void onActivityCreated(Bundle saved) {
    super.onActivityCreated(saved);
     input_text = (EditText) InputFragmentView.findViewById(R.id.input_field);

translate_button = (Button) InputFragmentView.findViewById(R.id.translate);


translate_button.setOnClickListener(new OnClickListener()
{
    @Override
    public void onClick(View view)
    {
        Log.d("Test", "onClickListener ist gestartet");
        Toast.makeText(getActivity().getApplicationContext(), "Test",        Toast.LENGTH_LONG).show();
        saveInString();

    }
});

because this methode called after all view have been created. you should read the life cycle of Fragment.