public Observable getLocaleChangedObservable() {
        return localeChangedObservable;
    }
If the Locale has been changed via {@link LocaleUtil#setUserLocale(Locale)} the stored formats need to be
refreshed. All formats which aren't originated from DataFormatter itself, i.e. all Formats added via
{@link DataFormatter#addFormat(String, Format)} and {@link DataFormatter#setDefaultNumberFormat(Format)}, need to
be added again. To notify callers, the returned {@link Observable} should be used. The Object in
{@link Observer#update(Observable, Object)} is the new Locale.

@return the listener object, where callers can register themselves
fastexcel-test/src/test/java/cn/idev/excel/test/temp/dataformat/DataFormatter1.java