android.speech.tts.TextToSpeech.setLanguage(java.util.Locale)' on a null object reference

My app crashes and in logcat I find the error

android.speech.tts.TextToSpeech.setLanguage(java.util.Locale)' on a null object reference

Here is my class :

public class cl_txt2speech {

    TextToSpeech txt2speech;
    Activity context;

    String txt2speech_current_language = "" ;
    boolean txt2speech_available = false ;

    //@Override
    protected void onCreate(Bundle savedInstanceState) {

        txt2speech = new TextToSpeech(context.getApplicationContext(), new TextToSpeech.OnInitListener() {
            @Override
            public void onInit(int status) {
                if (status != TextToSpeech.ERROR) {
                    txt2speech_available = true ;
                }
            }
        });
    }

    void txt2speech_change_language( String lang )
    {
        if( lang=="fr" )
        {
            txt2speech.setLanguage(Locale.FRANCE);
        }
        else if( lang=="en" )
        {
            txt2speech.setLanguage(Locale.UK);
        }
        else if( lang=="es" )
        {
            Locale locSpanish = new Locale("spa", "MEX");
            txt2speech.setLanguage(locSpanish);
        }
        txt2speech_current_language = lang ;
    }

    void txt2speech_speak( String lang , String txt )
    {
        if( lang != txt2speech_current_language ){ txt2speech_change_language( lang ); }
        txt2speech.speak(txt, TextToSpeech.QUEUE_FLUSH, null);
    }
}

and here is how I use it

cl_txt2speech txt2speech = new cl_txt2speech();
txt2speech.txt2speech_speak( "fr" , "test, 1 2 3" );

I don't understand what is the problem, I defined TextToSpeech txt2speech ; at the beginning.

edit : I did add some System.out.println() to trace what is happening, and it seems that the code in onCreate is never executed. So the problem must come from how I use my class.

from android.speech.tts.TextToSpeech.setLanguage(java.util.Locale)' on a null object reference