You can't, really: All that we can hear is that it is a Slavic accent: Russian and Serbian accent sounds absolutely the same in English.
They do not. For example, Russians devoice final consonants, while Serbs do not. There is vowel reduction in Russian but there isn't in Serbian. Serbs do not palatalize consonants before [i].
Some Russian vowels that are a bit like a mix of two different vowels (from my perspective).
Do you mean they are pronounced like diphtongs? Or what? Could you give some examples?