Ukraine

The Ukrainian system of names basically functions this way: If your name is Oleh Melnyk and you want to call your newborn child Nastia, what gets written in the documents is Anastasiia. Then, people will call that Nastia this way:

• If they have to be very formal, they call her Anastasiia Olehivna (this is the father's first name with a suffix)
• If they have to be formal, they call her Anastasiia Melnyk (this is Nastia's family name)
• If they have to be somewhat formal, they call her Anastasiia
• If they have to be informal, they call her Nastia

Every Anastasiia is always called Nastia by most people around her. And every Nastia has "Anastasiia" as their name in their official documents. Nastia's parents will never* call her Anastasiia. Not even when telling their friends what their newborn's name is. They will say "Look, this is our Nastia!"

The same applies to basically all other names as well. There are lists online for what name corresponds with which nickname and there is no simple pattern that you can reliably use to automatically turn a name's informal form into a formal form of the name or vice versa. For foreign names, -chka is a very common solution. When I lived in Ukraine, I would have ended up being Tuuchka, which is kind of funny because it means a small cute cloudlet, but people found that weird and just had to resort to always using my name as in documents, which made them feel kind of uncomfortable. If they cannot distinguish between whether the form they use is a formal or an informal one, their brain breaks a little.

Oh, and when I call my wife's phone from an unknown number, she answers with "Anastasiia ", but if I give her my phone and she knows she's talking to a friend of mine without knowing precisely whom, her first words in the phone are "Nastia ". And no, her father's name is not Oleh. Nor Melnyk. I just took those names randomly. Melnyk is the most common family name over there.

*) Never, except when they are super angry at her for some seriously bad mischief. Then they shout ANASTASIIA MELNYK, and she knows she in trouble. And if it's "ANASTASIIA OLEHIVNA, come here NOW!" then it means she immediately knows she's been caught after all for having killed her sibling three years ago, or something like that. And similarly, if they want to be just generally stern and not angry (although: almost angry), they can go with just "Anastasiia. Come here. Now."

There really isn't one singular way to derive shortened/informal forms from full names. Some names have multiple possible derivatives, too, and you'd probably need to just figure them out on a case by case basis.

If you want an extra formal way to address someone, you can use first name + patronym, like Ivan Petrovych (Ivan, son of Petro) which is often the default when speaking to elders or superiors. Addressing someone by their last name is rather rare, unless it's their preferred nickname or if you want to emphasize on it.

As another comment mentioned, there also isn't really a pattern to masculine/feminine versions of names either. Some names have common versions of both genders (Oleksandr/Oleksandra), for some one gender is more commonly used (for example, masculine Bohdan is more common than feminine Bohdana) and some only have one gender version (like Mykyta that you mentioned).

If you have questions about usage of specific names or name forms, I'd be happy to answer!

There is no "feminizing" in the Ukrainian language. There are different names for men and women. And a few are very similar like Olexandr for men and Olexandra for women. Still these are different names.

-Ka is used, indeed. You can make Mykytka from Mykyta. But the usage is not straightforward, you won't be able to use it without knowing (or "feeling") the language. Olexandr won't be Olexandrka. But Sanyok or Shura.