Alin
[name]Cezar[/name]
[name]Emil[/name]
Ion
Ilie
[name]Ioan[/name]
[name]Mihai[/name]
Radu
[name]Vali[/name]
[name]Bogdan[/name] (more than four letters, but might still work for you)
It’s actually tougher than I thought to find names with only 3-4 letters.
[name]Jago[/name]
[name]Benno[/name]
[name]Dirk[/name]
[name]Ivo[/name]
[name]Uri[/name]
[name]Ingo[/name]
[name]Piero[/name]
[name]Ivan[/name]
[name]Arlo[/name]
[name]Igor[/name]
Udo
Mirko
[name]Nils[/name]
[name]Iago[/name]
[name]Dante[/name]
[name]Inigo[/name]
Arne
Emil
Marcel
Alain
Boris
Karl
Franz
Lev
Oleg
Timo
Rudy
Johan
Gino
Rurik
Dario
I speak Russian fluently as I am half-Ukrainian so I would give you some suggestions really used there(sorry for repeats) and traditional nicknames(keep in mind we never use nicknames as given names)
Aleksey - Lyosha
Aleksander - Sasha, Sanya, Shura
Boris - Borya
Bohdan - Bodya, Dan
Constantine(rhymes with green) - Costya
Dmitriy - Dima
Evgeniy - Jenya
Elisey - Eliseyka
Foma(fo-muh)
Gleb
Goreslav - Slavs
Iliya
Innokentiy - Kesha
Leonid - Lyonya
Lev
Maksim - Maks, Maxik
Naum(nuh-oom)
Oleg - Olegka
Pavel - Pasha
Radimir - Rad
Radoslav - Slava
Severian - Seva
Stanislav - Slava, Stas
Svyatopolk - Svyatik
Timur(tee-moor) - Timurka
Vadim - Vadik
Vladimir - Vova, Volodya
Vladislav - Vlad, Slava
Vladlen - Vlad
Zinoviy - Zenik
Almost none are very short but we don’t use short names. Gleb, Lev, Naum, Oleg are 3-4 letters and the most amount of short “Russian” names usually considered are just nicknames in Russian.
This is just a sample from wonderful word of Russian names. If you are interested, message me and I will give you some more ideas.