italian translation update and a few questions

Hi,
I am updating the italian translation of pgAdminIII, but I found a few
sentences that I do not understand. Would you please explain what are
their meanings?

ANALYZE base threshold
ANALYZE scale factor
Acks outstanding
Could not open the message source registry key.
Could not set the event message file registry value.
Covering index
Do instead
Heap Blocks Hit
Histogram Bounds
Index Blocks Hit
Left Table Columns
Link symbol
Security of definer
Set by test
Toast Blocks Hit
Unexpected empty cache line: dataSet already closed.
VACUUM base threshold
VACUUM cost delay
Can forward
Group Role

And, why should "WITH ADMIN OPTION" be translated if it is SQL language?

Moreover, there are a few sentences for translators, like:

#: src/frm/frmMain.cpp:724
msgid ""
"Translator attention: must match backend translation!no pg_hba.conf
entry for"
msgstr ""

How should these sentences translated? Should I remove the first part
and look for the translation of "no pg_hba.conf entry for" in the
postgresql po file?

Last question: are "Server" and "Backend" used for the same object?

Thanks,
Giuseppe