Nice, finally something to use some dynamic programming!

If you want to view kata that you have solved, you can do so in your profile. There it shows you which languages you completed for that kata. It will give you the basic functionality that you are asking for.

While it would be great to have kata I've completed show up in the searchable kata list based off of which language you have selected, due to the complexity of different configurable filters, it would require some rework to support "kata i've completed" at a language level. Its not likely to change any time soon.

Under "Kata" you can chose different languages and see the katas in the language. You can also chose if you see the katas you haven't solved yet.
If I chose an other language(e.g. Javascript) all katas I solve in the other language (e.g. Java) is already solved. So it is very difficult to find out which katas I have solved in one language and which in another.

I guess currently the clan system is just a grouping of users not really a 'clan' feature.
you can see everyone in the clan on the home page where it will show everyone with the same clan tag and order them by honor ranking.

Why can't we have a clan URL with a scoreboard/users? We have to each follow each other, and that's annoying