What kind of convert for password when using Angular and Cache 2017.1?

In our language we have scandic letters like ä (a with two dots on it).

In Angular we use login like this:

let headers = new Headers();

password = Base64.fromBase64(password);

headers.append('Authorization', 'Basic ' + Base64.encode(username + ':' + password));

let options = new RequestOptions({ headers: headers, withCredentials: true });

return this._http.get(_param.baseUrl + this._loginUrl, options)

.map((res: Response) => {

It works, but not with these letters.

In other cases we convert data on server side like

set:tValue'="" tValue=$ZCONVERT(tValue,"I","UTF8")
 

but in this case we can't do this on server side, but should do on client side, but how?

PS. To ZAUTHENTICATE we should get char(228), but get char(195).