Naval oranges are high in calcium and are often listed on tortoise food lists since they are also a great source of vitamin A and other nutrients. I am not an expert on Russians but I would have a hard time saying 'never'- although even for my Red-foots I would not offer it often.
Once in a blue moon, it wouldn't be too bad. Personally I just flat out never give fruit to my Russians, Stars, Sulcatas or Greek - my Redfoots, Hingebacks, Manouria and Box turtles get some fruit weekly.
Cooper gets watermelon once in a great while and only very small amounts. He loves it so much, but he will never get all he wants of it, to much is a bad thing I think.
We have a small orange tree that fruit hangs low on... And RV loves the color orange. We've found oranges with bite marks on them, but she doesn't like them apparently, spits them out pronto and doesn't go back. It hasn't put her off the color orange in any way, and she's pretty much sworn off fruit from the trees....
we had an apricot tree (didn't take the heat or picked up a virus or something). when it was dropping fruit, we had a hard time beating RV to the gold on the ground.......