getActivity() return null

The best to prevent your activity being null is to keep activity reference when onAttach is called and use the activity reference wherever needed.

Ex:

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    mContext = context;
}

@Override
public void onDetach() {
    super.onDetach();
    mContext = null;
}

And Now inside you show toast as

Toast.makeText(mContext, mContext.getResources().getString(R.string.no_rides_found), Toast.LENGTH_SHORT).show();

Edited:
onAttach(Activity) is depreciated & now onAttach(Context) is being used

Following this tutorial I tried to add French language in my app which is currently in English, (Not by changing the system language)

I added the translation in a separate strings file

It seems the problem is in my code. I’m not sure If I have to rewrite the same function in all my activity for it to work here is the code for switching language

Edit 2 : commenting this line fix the crash issue but the language is not updating.
Only the toast messages change to french but the UI layout isn’t

//Toast.makeText(getActivity(), getActivity().getResources().getString(R.string.no_rides_found), Toast.LENGTH_SHORT).show();

ActivtyRide

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //loadLocale before setContentView
    loadLocale();
    setContentView(R.layout.activity_ride);
    ActionBar actionBar = getSupportActionBar();
    actionBar.setTitle(getResources().getString(R.string.app_name));

private void setLocale(String lang) {
    Locale locale = new Locale(lang);
    Locale.setDefault(locale);
    Configuration config  = new Configuration();
    config.locale = locale;
    getBaseContext().getResources().updateConfiguration(config, getBaseContext().getResources().getDisplayMetrics());
    SharedPreferences.Editor editor = getSharedPreferences("Settings", MODE_PRIVATE).edit();
    editor.putString("My_Lang", lang);
    editor.apply();
}
public void loadLocale(){
    SharedPreferences prefs = getSharedPreferences("Settings", Activity.MODE_PRIVATE);
    String language = prefs.getString("My_Lang", "");
    setLocale(language);
}

And here is the Activity that causing me the crash

FragmentAllRides

 //ASYNTASK Getting Data From Server/////////////////////////////////////
public class GetAllRides extends AsyncTask<String, Void, String> {

    @Override
    protected void onPreExecute() {
    }

    @Override
    protected String doInBackground(String... params) {

    }


    @Override
    protected void onPostExecute(String s) {

        rotateLoading.stop();
        relativeLayout.setVisibility(View.GONE);

        if (server_check) {


            if (server_response.equals("1")) {


                if (driver_name.length > 0) {


                    adapter = new AllRidesAdapter(getActivity(),
                            arrayList);

                    listView.setAdapter(adapter);


                    //filtering data
                    EtSearch.addTextChangedListener(new TextWatcher() {
                        @Override
                        public void beforeTextChanged(CharSequence charSequence, int start, int count, int after) {
                        }

                        @Override
                        public void onTextChanged(CharSequence charSequence, int start, int before, int count) {

                            if (search_value.equals("source")) {
                                adapter.getFilter().filter(charSequence);
                            } else if (search_value.equals("destination")) {
                                adapter.getFilter2().filter(charSequence);
                            } else {
                                Toast.makeText(getActivity(), "ass", Toast.LENGTH_SHORT).show();
                            }
                        }

                        @Override
                        public void afterTextChanged(Editable editable) {
                        }
                    });


                } else {
                    Toast.makeText(getActivity(), server_response_text, Toast.LENGTH_SHORT).show();

                }
                
            } else {

                Toast.makeText(getActivity(), getActivity().getResources().getString(R.string.no_rides_found), Toast.LENGTH_SHORT).show();
            }

        } else {
            Toast.makeText(getActivity(), getActivity().getResources().getString(R.string.server_error), Toast.LENGTH_SHORT).show();

        }
    }
}

Logcat

 java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources androidx.fragment.app.FragmentActivity.getResources()' on a null object reference
    at com.devqx.covoiturage.Ride.Home.FragmentAllRides$GetAllRides.onPostExecute(FragmentAllRides.java:672)
    at com.devqx.covoiturage.Ride.Home.FragmentAllRides$GetAllRides.onPostExecute(FragmentAllRides.java:464)
    at android.os.AsyncTask.finish(AsyncTask.java:755)

Any ideas ?