How to solve the problem with the encoding when sending an email?

Question

Android

There is an application, in it a contact form, when receiving a letter to the post office, the Russian language is in the form of hieroglyphs.
How to set encoding?

public class ContactActivity extends AppCompatActivity {
    private static final String TAG = ContactActivity.class.getSimpleName();
    private ProgressDialog pDialog;
    private Activity activity;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_contact);

        activity = this;

        pDialog = new ProgressDialog(activity);
        final EditText your_name        = (EditText) findViewById(R.id.your_name);
        final EditText your_email       = (EditText) findViewById(R.id.your_email);
        final EditText your_subject     = (EditText) findViewById(R.id.your_subject);
        final EditText your_message     = (EditText) findViewById(R.id.your_message);

        //Forcing RTL Layout, If Supports and Enabled from Const file
        Utils.forceRTLIfSupported(this);

        //Setting Up Support Toolbar
        final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        setTitle(getString(R.string.contact_form));

        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                onBackPressed();
            }
        });


        Button post_message = (Button) findViewById(R.id.post_message);
        post_message.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Boolean onError = false;
                final String email = your_email.getText().toString();
                if (!isValidEmail(email)) {
                    onError = true;
                    your_email.setError(getString(R.string.error_invalid_email));
                }

                final String name = your_name.getText().toString();
                if (!isValidString(name, Const.ContactNameValidationLimit)) {
                    onError = true;
                    your_name.setError(String.format(getString(R.string.error_length), Integer.toString(Const.ContactNameValidationLimit)));
                }

                final String subject = your_subject.getText().toString();
                if (!isValidString(subject, Const.ContactSubjectValidationLimit)) {
                    onError = true;
                    your_subject.setError(String.format(getString(R.string.error_length), Integer.toString(Const.ContactSubjectValidationLimit)));
                }

                final String message = your_message.getText().toString();
                if (!isValidString(message, Const.ContactMessageValidationLimit)) {
                    onError = true;
                    your_message.setError(String.format(getString(R.string.error_length), Integer.toString(Const.ContactMessageValidationLimit)));
                }
                
                if (!onError) {
                    pDialog.setTitle(getString(R.string.contact_form));
                    pDialog.setMessage(getString(R.string.contact_form_post_message));
                    pDialog.show();

                    //Requesting The Story
                    String url = Const.URL_BLOG + Const.URL_BLOG_API + Const.URL_SEND_MESSAGE + "?t=" + System.currentTimeMillis();

                    // making fresh volley request and getting json
                    StringRequest sr = new StringRequest(Request.Method.POST, url, new Response.Listener<String>() {
                        @Override
                        public void onResponse(String response) {
                            pDialog.hide();
                            JsonParser jsonParser = new JsonParser();
                            JsonObject jo = (JsonObject) jsonParser.parse(response);

                            try {
                                JSONObject obj = new JSONObject(response);
                                if (obj.has("error")) {
                                    String error = obj.getString("error");
                                    Toast.makeText(activity, error, Toast.LENGTH_LONG).show();
                                } else {
                                    //parseJsonFeed(response);
                                    your_message.setText("");
                                    your_name.setText("");
                                    your_email.setText("");
                                    your_subject.setText("");
                                    Utils.showAlertDialog(activity, getString(R.string.contact_form), getString(R.string.contact_posted));
                                }
                            } catch (Throwable t) {
                                t.printStackTrace();
                            }
                        }
                    }, new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {
                            pDialog.hide();
                        }
                    }) {
                        @Override
                        protected Map<String, String> getParams() {
                            Map<String, String> params = new HashMap<String, String>();
                            params.put("contact_name", name);
                            params.put("contact_email", email);
                            params.put("contact_subject", subject);
                            params.put("contact_message", message);
                            return params;
                        }

                        @Override
                        public Map<String, String> getHeaders() throws AuthFailureError {
                            Map<String, String> params = new HashMap<String, String>();
                            params.put("Content-Type", "application/x-www-form-urlencoded");
                            params.put("ApiKey", Const.AuthenticationKey);
                            return params;
                        }
                    };

                    // Adding request to volley request queue
                    AppController.getInstance().addToRequestQueue(sr);
                }
            }
        });
    }

    @Override
    public void onResume() {
        super.onResume();
        //Get a Tracker (should auto-report)
        if (Const.Analytics_ACTIVE) {
            AnalyticsUtil.sendScreenName(this, TAG);
        }

    }

    @Override
    protected void onStart() {
        super.onStart();
        GoogleAnalytics.getInstance(ContactActivity.this).reportActivityStart(this);
    }

    @Override
    protected void onStop() {
        super.onStop();
        GoogleAnalytics.getInstance(ContactActivity.this).reportActivityStop(this);
    }


    // validating email id

    private boolean isValidEmail(String email) {
        String EMAIL_PATTERN = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@"
                + "[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";

        Pattern pattern = Pattern.compile(EMAIL_PATTERN);
        Matcher matcher = pattern.matcher(email);
        return matcher.matches();
    }

    // validating information
    private boolean isValidString(String pass, int length) {
        if (pass != null && pass.length() > length) {
            return true;
        }
        return false;
    }
}