Magento Adding a new Language?
What I usually do to add russian language:
- Add store view and assign russian locale to it like it is done in your link
- Download russian translation by us (ET) from this topic (Niro comment) and install it manually
That's it!
I know that there are some cases similar to yours and usually it means that you have tried to install translation from Magento Connect. The problem is in permissions. It is much easier and safer to install it manually.
And why unofficial translation? Well, because official one is too bad.
And if this doesn't help you, it would be great to see, what your error looks like. It will be easier to find the source of the problem.
Some locale packages seem to be packed wrong. After installing instead of expanding into their locale folders such as ru_RU, they are expanded in locale, which obviously is wrong. I have met few of those. Creating corresponding locale folder and moving the files in it usually solves the problem. Don't forget to flush cache after that.