Actually, it's because the game was never fully translated.
The tutorials for each faction were the only parts of the game that had English voice acting, though this was removed I believe when the EU and NA servers were merged. Might have been before or after though.
I believe the developers never went forward with a full English because
A) It's one of the most time consuming and expensive endeavors for a company to make, as committing to a full translation means delaying the release of a game until all voiced dialogue has been recorded and properly placed in game.
B) The popularity of the game. It's not an unknown fact (well, more of to the fans) that Allods had one of the worst releases an MMO could ever have internationally, losing most of the NA playerbase right around the official release (not to discount the non-Russian European community, but for the most part the NA market is considered one of the largest and is a reliable scale on whether a game will be successful or not).
Props to the developers for still believing in an international market, but the game has yet to recover from the issues at release.
It shouldn't be a deal breaker that the game chooses to have translated text and Russian dialogue. There are a number of games that didn't localize voiced lines in game due to the time and cost expense.