Looking a recommendation for my criteria.

I need to create a file for different countries and looking at the best naming strategy for this. 

I am working with .net 4.5. So example I need to create a file with Russian data, should it be named

```
rus_myfile.txt [ThreeLetterISOLanguageName]

ru_myfile.txt [TwoLetterISOLanguageName]

```

or another?

Is there any standard for naming conventions based on the .Net [CultureInfo](http://msdn.microsoft.com/en-us/library/system.globalization.cultureinfo.aspx) object? Any gotchas in this area?