Debugging language detection in Play framework on Heroku

gistfile1.java

  public static Result acceptedLanguages() throws IOException {
        Map<String, Object> stuff = new HashMap<>();
        stuff.put("profilepage.profile.button.connect", Messages.get("profilepage.profile.button.connect"));
        stuff.put("acceptedLanguages header", request().headers().containsKey("Accept-Language")?request().headers().get("Accept-Language")[0]:"non-existant");
        stuff.put("play.mvc.Http.Context.current().request().cookies()", Http.Context.current().request().cookies());
        List<Lang> availables = Lang.availables();
        Collection<Locale> transform = Collections2.transform(availables, new Function<Lang, Locale>() {
            @Override
            public Locale apply(Lang lang) {
                return lang.toLocale();
            }
        });

        stuff.put("play.i18n.Lang.availables() to locales", transform);
        stuff.put("play.mvc.Http.Context.current().request().headers()", play.mvc.Http.Context.current().request().headers());
        stuff.put("play.mvc.Http.Context.current.get()", play.mvc.Http.Context.current.get());
        stuff.put("play.mvc.Http.Context.current().lang()", play.mvc.Http.Context.current().lang());
        stuff.put("play.mvc.Http.Context.current().lang().toLocale()", play.mvc.Http.Context.current().lang().toLocale());
        List<Lang> value = request().acceptLanguages();
        Collection<Locale> locales = Collections2.transform(value, new Function<Lang, Locale>() {
            @Override
            public Locale apply(@Nullable Lang lang) {
                if (lang == null)
                    return null;
                return lang.toLocale();
            }
        });

        stuff.put("acceptedLanguages to locale", locales);

        ObjectMapper mapper = new ObjectMapper(  );

        mapper.configure( SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS, false );
        return ok(mapper.writeValueAsString(stuff)).as("application/json");
    }