private boolean isLanguageAllowed(String languageKey) {

        // If no list is provided, all languages are implicitly available
        if (allowedLanguages == null)
            return true;

        return allowedLanguages.contains(languageKey);

    }
Returns whether a language having the given key should be allowed to be
loaded. If language availability restrictions are imposed through
guacamole.properties, this may return false in some cases. By default,
this function will always return true. Note that just because a language
key is allowed to be loaded does not imply that the language key is
valid.

@param languageKey
    The language key of the language to test.

@return
    true if the given language key should be allowed to be loaded, false
    otherwise.
guacamole/src/main/java/org/apache/guacamole/extension/LanguageResourceService.java