Add a few languages...
Hi Steve, based on the amount of related ideas I'm sure this is nothing novel, but I have been studying a fair amount of minority languages similar to ones I already speak, and no reading aid with vocabulary tracking works with them natively*.
Namely:
Low German/Saxon
West Frisian (*LanguageCrush actually does support Frisian)
Faroese
Northern Sámi
Attempts to use them in tools that don't really support them, e.g., Readlang or LingQ just don't work very well, and I don't find the reader of configurable tools like LWT/Lute nearly as good as those mentioned above.
You'd have a lifetime sub from at least me if either those languages were selectable in the list or there was a way for me to configure custom languages myself.
If it doesn't happen then oh well - my hacky calibre solution will do :).