Add "Language Rank Up" focus

[DvitryG]

Problem: when a user with a medium/high rank begins to learn a completely new language, existing recommendation algorithms stop working properly.
“Fundamentals” quickly become irrelevant, “Rank Up” offers tasks that are too early to take on with the current level of knowledge, and so on.

Since each user has a rank for each language they study:

adding an algorithm similar to “Rank Up” but for the currently selected language will allow you to automatically build a smooth learning curve, avoiding situations where the user needs to independently search for tasks that are suitable in complexity

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There was already a question on this topic (#2940), but in this case I decided to offer my own solution.

Of course, you can come up with something smarter, since it is obvious that most people will learn new languages faster if they know other languages. But this solution will be a great start in this direction.

[DvitryG]

I really liked "Rank Up" when I first started using codewars, but after I started learning different languages, it lost its meaning for me, since my overall rank is higher than the rank for a single language