The Game Editor on this site is a perfectly good PGN editor - select More at top of any page & click on Analysis Board & Editor on the drop-down menu.
Select 'Game Editor' mode & you can then paste in your PGN file - it's not possible to directly import a PGN file into the Editor or save it (open it first in any text editor but remember to select the 'all file types' option). Then you can step through the moves & add/edit/delete any of the comments.
When you've finished, you can save the PGN by choosing the 'Copy PGN' option & then copy/paste it back into your text editor & from there save it to your PGN's folder ?
I don't know whether it will correctly display comments in Russian however ! But you could translate the comments one at a time into a language that does display o/k by using Google translate:-
http://translate.google.co.uk/?hl=en&tab=wT
Dear chess community!
Please help me with opening PGN files on my MAC. Also I want to view comments in Russian already recorded in PGN archive.
Have tried Shredder, but it doesn't display correctly Russian font.
Many thanks for you help!
P.s. may be there is some online pgn viewers, which could save my comments to reviewed pgn archives?