Utilizing ASCII-characters would be a much easier solution if you ask me.
This function should be able to do what you want, and more.
FString GenerateRandomCharacters(uint32 AmountOfCharacters) {
FString Result = "";
for (uint32 = 0; i < AmountOfCharacters; ++i) {
Result += FMath::RandRange(0, 127);
}
return Result;
}
Reference:
http://www.bibase.com/images/ascii.gif
Haven’t tried it out, but it should work 