As for the Russian, it's a translator discretion thing, and personally I agree with their choices. It helps us read it in much the same way natives speakers do when reading in Japanese. Alphabets are difficult things, to work with, and the more you fudge with them in translation the harder it gets to accurately depict the pronunciation, and at an even deeper level the etymology gets lost a bit too. Sooo, for a general audience, leaving them as is is best I think.
I think I wasn't clear - or you'd not have mentioned it helps us read it the same way as native Japanese do, or etymology - they don't enter in to what I meant.
I don't know what the translators have added or changed but I'm suggesting the original would've been better written like-
большое спасибо (the Russian text) then in small besides it, ボルショイエ・スパシボー or something similar - they still don't know what that means unless they happen to know the Russian words - and replace that in our translated version with 'bol'shoye spasibo'. Then, if you wish your readers to know what she is actually saying - the original would include どうも有難う in bigger font beside it - and our translated version 'thank you so much' or whatever.
All I'm endorsing is whenever a manga wants to use words from a foreign language that are written in an alphabet the readers can't even pronounce because they don't know the letters - even if you aren't going to give a translation of the word because the other characters in the scene don't know what's being said either- you should STILL write a - basically a 'sound effect' of the word if you will - so we 'hear' what the people in the scene heard too- and like them we won't know what it means but might at least think, 'that sounded Russian'.
Without that pronunciation sub script, we don't have any idea what words she actually spoke- just their meaning, and I want to be able to 'hear' those Russian words, and I can't if I have no clue of what was said.
I hope that was clearer.