Translation in Core , Plugin and Theme Update wordpress

I’m Curious about translations in update transient for Core , Plugin and Theme Updates.

I got this from _site_transient_update_core in wp_option table in this why translations array is always empty ? I have deleted all .mo , .po and .pot files even this translations array is empty ! can you explain when i will get translation in core update ? I’ve been searching this for 3 days.

stdClass Object
(
[updates] => Array
(
[0] => stdClass Object
(
[response] => upgrade
[download] => http://downloads.wordpress.org/release/wordpress-4.2.2.zip
[locale] => en_US
[packages] => stdClass Object
(
[full] => http://downloads.wordpress.org/release/wordpress-4.2.2.zip
[no_content] => http://downloads.wordpress.org/release/wordpress-4.2.2-no-content.zip
[new_bundled] => http://downloads.wordpress.org/release/wordpress-4.2.2-new-bundled.zip
[partial] =>
[rollback] =>
)

[current] => 4.2.2
[version] => 4.2.2
[php_version] => 5.2.4
[mysql_version] => 5.0
[new_bundled] => 4.1
[partial_version] =>
)

)

[last_checked] => 1432540495
[version_checked] => 3.7.2
[translations] => Array
(
)

)