After Update to IOS 13.5.1 the default bulgarian keyboard has wrong positioned keys ...

Before updating to the latest iOS 13.5.1 as told on your post what was your earlier iOS version. Then you can look into the iOS changes that has happened between the earlier version on your iPhone and this new version that you have updated now. 

This will give you a broader idea of the issue, if it is directly linked to the iOS version or is triggered by something else.

Because iOS 13.5.1 was only for security update, you may probably be carrying a legacy issue from previous iOS versions.

Remove the keyboard and add again.

mep253 wrote:

default (not phonetic) bulgarian keyboard has wrong positioned keys and even russian letters!

Could you explain with specific examples? Aside the the position of the Б letter, the layout in your picture seems to be the same as Bulgarian Standard, and I don't see any letters which are not Bulgarian.

https://en.wikipedia.org/wiki/Keyboard_layout#/media/File:Bulgarian_BDS_layout.svg

Could you provide a picture of what the layout is supposed to look like?

I doubt it’s connected to other problem then this update as all my friends who upgraded (including me) have the same issue. So yes the upgrade broke the Bulgarian keyboard.