twofacedv wrote:
So the question is: can I add the support of Windows standart encodings for that situations not to happen?
It is already there. MacOS X fully supports Russian and most other languages too. You just happened to pick two worst case scenarios.
For Guitar Pro 5, there is nothing you can do but contact them and report the bug. That is a 3rd party product and obviously has trouble with Russian. It seems to be a cross-platform program and that is likely the reason.
Text files are always difficult. There is nothing about a text file that indicates what encoding it is. You would have to open it in something like TextWrangler that might be able to detect the encoding. If all else fails, you could try various, likely encodings until it was readable. Once you get there, save the file as UTF-8 and you won't have any more problems with it.