public Set<String> getLanguageKeys() {
        return Collections.unmodifiableSet(resources.keySet());
    }
Returns a set of all unique language keys currently associated with
language resources stored in this service. The returned set cannot be
modified.

@return
    A set of all unique language keys currently associated with this
    service.
guacamole/src/main/java/org/apache/guacamole/extension/LanguageResourceService.java