For me the feature that sets Wokabulary apart from all others is the ability to tag words and quiz yourself on select tags.
However, as my list of tags increases, it becomes more difficult to scroll through them and find the ones I need. For example, I am adding the tags “AN” and “Preposition” and “Verb” to refer to the German verbs that require an “an”. It would be amazing to be able to nest the tag “AN” within “Preposition”. The same for “Feelings” within “Noun” (for example). Perhaps this can be achieved in the left menu, i.e. clicking on “Noun” would reveal “Feeling”, “Kitchen”, “Politics”, etc.
At the bare minimum, it would be nice to be able to sort the tags beyond alphaberical order.