Sergey Biryukov

Up to 3.3.x, Russian WordPress packages had some CSS fixes to make room for translated strings in the admin menu and other UI elements.
In 3.4 and 3.5, those fixes were merged into core (see <a href="https://core.trac.wordpress.org/ticket/19603" rel="nofollow ugc">#19603</a> and <a href="https://core.trac.wordpress.org/ticket/20975" rel="nofollow ugc">#20975</a>). However, obsolete language files are not deleted during an automatic update (see <a href="https://core.trac.wordpress.org/ticket/20974" rel="nofollow ugc">#20974</a>). Unfortunately, this causes the admin menu to disappear when directly updating from 3.1.x or an older version to the latest releases from <a href="https://ru.wordpress.org/" rel="nofollow ugc">ru.wordpress.org</a>.
The list of obsolete files:
<pre><code>wp-content/languages/ru_RU.php
wp-content/languages/ru_RU.css
wp-content/languages/ru_RU-ie.css
wp-content/languages/ms-ru_RU.css
</code></pre>
The best option is just to remove them manually via FTP. If for some reason you can’t do that, you can try this plugin, which restores the admin menu by unhooking <code>ru_accomodate_markup()</code> function and attempts to remove the obsolete files.
After installing and activating the plugin, try deactivating it. If you still see the admin menu, you can safely remove the plugin, its job is done. If you can’t see the admin menu, activate the plugin again.

Restore Admin Menu (ru_RU)

Restores the admin menu when updating from 3.1.x or an older install to the latest release from ru.wordpress.org.

Some alternative (unofficial) Russian localization teams modify the automatic update procedure to download WordPress core packages from their own hosts. The problem is that they systematically fail to deliver updates on time (even security updates) and currently provide no visible support for their releases.
This plugin allows you to update any outdated Russian WordPress package to the latest release from <a href="https://ru.wordpress.org/" rel="nofollow ugc">ru.wordpress.org</a>.
You can safely remove the plugin after the update.
Thanks to AlexPTS for the idea.

Restore Automatic Update (ru_RU)

Allows you to update any outdated Russian WordPress package to the latest release from ru.wordpress.org.

Restore Admin Menu (ru_RU) vs Restore Automatic Update (ru_RU)