How do Jehovah Witnesses explain differences between NWT and Hebrew/Latin/Greek in Zechariah 12:10 and Acts 20:28? How do Jehovah Witnesses explain the differences between the New World Translation and Latin/Greek, specifically in these two Bible verses?

(1) Zechariah 12:10

King James Version (KJV)


  And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for his only son, and shall be in bitterness for him, as one that is in bitterness for his firstborn


New World Translation (NWT)


  I will pour out on the house of David and on the inhabitants of Jerusalem the spirit of favor and supplication, and they will look to the one whom they pierced,+ and they will wail over him as they would wail over an only son; and they will grieve bitterly over     him as they would grieve over a firstborn son 


Latin Vulgate by Jerome in 382AD


  ..et effundam super domum David et super habitatores Hierusalem spiritum gratiae et precum et aspicient   ad me quem confixerunt et plangent eum planctu quasi super unigenitum et dolebunt super eum ut doleri solet in morte primogeniti


(There is no word indicating 'the one'.)

LXX Septuagint — Greek translation of Hebrew in 132BC


  καὶ ἐκχεῶ ἐπὶ τὸν οἶκον Δαυιδ καὶ ἐπὶ τοὺς κατοικοῦντας Ιερουσαλημ πνεῦμα χάριτος καὶ οἰκτιρμοῦ καὶ ἐπιβλέψονται πρός [TOWARD] με [ME] ἀνθ’  ὧνκατωρχήσαντο καὶ κόψονται ἐπ’ αὐτὸν κοπετὸν ὡς ἐπ’ ἀγαπητὸν καὶ ὀδυνηθήσονται ὀδύνην ὡς ἐπὶ πρωτοτόκῳ (No word indicating 'the one')


(2) Acts 20:28

King James Version (KJV)


  Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood.


New World Translation (NWT)


  Pay attention to yourselves and to all the flock, among which the holy spirit has appointed you overseers,+ to shepherd the congregation of God, which he purchased with the blood of his own Son"


Latin Vulgate by Jerome in 382AD


  .adtendite vobis et universo gregi in quo vos Spiritus Sanctus posuit episcopos regere ecclesiam Dei quam adquisivit sanguine suo.


(There is no word translatable as 'son'.)

Greek New Testament


  Προσέχετε { οὖν ♦ ἑαυτοῖς καὶ παντὶ τῷ ποιμνίῳ, ἐν ᾧ ὑμᾶς τὸ πνεῦμα τὸ ἅγιον ἔθετο ἐπισκόπους, ποιμαίνειν τὴν ἐκκλησίαν τοῦ {κυρίου καὶ ♦ - } θεοῦ, ἣν περιεποιήσατο διὰ τοῦ { ἰδίου [OWN] αἵματος ♦ αἵματος τοῦ ἰδίου [OWN]}.


(There is no word translatable as 'son'.)

Note

Upon further research, I found the Dead See Scrolls segment that contains Zechariah 12:10  and, in trying to identify the Hebrew words in the English parallel, I am noticing what seems to be an aleph and tau (the first and last letters of the Hebrew alphabet) right after “inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon...” and before “and they shall mourn for him, as” as seen in this picture. Does anyone know what the aleph and tau (if that’s what they are), are doing there?

Note

FYI, I re-posted this question on hermeneutics.se, as two separate questions as suggested by Affable Geek:

On Zech 12:10 https://hermeneutics.stackexchange.com/questions/7604/how-do-jehovah-witnesses-explain-differences-between-nwt-and-latin-hebrew-greek

On Acts 20:28 https://hermeneutics.stackexchange.com/questions/7605/how-do-jehovah-witnesses-explain-differences-between-nwt-and-latin-greek-on-acts
The bible many times attributes actions to God as if he did them directly, when it is actually that he allowed it or had someone else do it. This is similar to a foreman saying that he build a house even though he didn't even hammer in one single nail. In simple terms, these scriptures are similar to that.
Below I have quoted an old Watchtower article that explains Zechariah 12:10.
Also here is a link to an appendix to the NWT that explains why Acts 20:28 was translated the way it is: http://wol.jw.org/en/wol/d/r1/lp-e/1001060098

Watchtower 1953 8/15 p. 511 - Questions From Readers
● Zechariah 12:10 states: “They shall look upon me whom they have pierced, and they
shall mourn for him, as one mourneth for his only son, and shall be in
bitterness for him, as one that is in bitterness for his firstborn.”
Jehovah is the speaker, and it sounds as though he was the one pierced
instead of Jesus. Some argue this proves that Jehovah and Jesus are
one in a trinity. So how is Zechariah 12:10 to be explained?—R. B.,
New York.
To avoid what seems to be a piercing of Jehovah some of the
later Hebrew manuscripts read “look upon him whom they have pierced”,
rather than “look upon me whom they have pierced”. At first these late
Jewish manuscripts show this in the Keri, or corrected reading in the
margin; but eventually in some manuscripts the change was brought up
into the body of the text itself. Rotherham’s translation, on the
basis of these late manuscripts, offers in a footnote “him” as an
acceptable reading in place of “me”. So does the American Standard
Version. Some modern translations, such as Moffatt and An American
Translation and Revised Standard Version, use “him” instead of “me” in
the main body of the text itself. However, the oldest and best Hebrew
manuscripts read “me” rather than “him”.
As far as literal piercing is
concerned, this occurred in the case of Christ Jesus, and at John
19:37 the prophecy of Zechariah 12:10 is quoted and applied to Jesus:
“They will look upon the one whom they pierced.” (NW) They did not
literally pierce God, who was in heaven and to whom Jesus spoke when
he was on the torture stake. (Matt. 27:46; Luke 23:46) God could not
die, and then resurrect himself. (Ps. 90:2) Yet inasmuch as Jesus
Christ was Jehovah’s representative who became “the exact
representation of his very being”, in piercing Jesus they could be
said to be piercing Jehovah. (Heb. 1:3, NW) When sending out his
followers to preach Jesus said: “He that receives you receives me
also, and he that receives me receives him also that sent me forth.”
(Matt. 10:40, NW) This shows that in receiving Jesus we receive
Jehovah who sent him. In like manner, to pierce Jesus is to pierce
Jehovah who sent him. It does not prove Jesus and Jehovah are one, any
more than it proves Jesus and his followers are literally one. In
another case Jehovah showed that to reject his representative is to
reject Him. When Samuel was Jehovah’s appointed judge over Israel the
people came requesting a king instead of a judge. Samuel was
displeased when they said: “Give us a king to judge us.” But Jehovah
told Samuel: “They have not rejected thee, but they have rejected me.”
(1 Sam. 8:4-7, AS) In rejecting Jehovah’s representative they rejected
Jehovah, in effect; but this did not make Samuel one with Jehovah in a
trinity.
Some of those used as tools to accomplish Jesus’ impalement realized
their mistake and became frightened; the crowds that had sanctioned
the piercing smote their breasts when they saw their blunder, and
later some involved ones repented and followed Christ. (Matt. 27:54;
Luke 23:47, 48; Acts 2:23, 36-42) But the only bitterness and mourning
that hit the religious instigators of the piercing was when things did
not work out fully for their selfish interests. The ones who truly
mourned were his faithful followers. (Luke 24:17) But as Zechariah
12:10 also foretold, about this time Jehovah’s spirit was poured out
upon the faithful remnant of natural Israel, at Pentecost. So the text
had its miniature fulfillment.
At the second presence of Christ Jesus the complete fulfillment takes
place. His followers are persecuted and jailed and some are killed,
and the work of announcing Jehovah’s King and kingdom is pierced and
killed. These things done to Christ’s work and followers are counted
as done to him; the persecutors are charged with piercing him. Any
mourning by them is in selfish fear when they see coming upon them the
dire consequences of their acts. The only true mourning is on the part
of Jehovah’s people who had allowed themselves to fall short of their
duties and be taken captive in Satan’s worldly system and made
inactive in Jehovah’s service. But Jehovah comes to the rescue of this
remnant of spiritual Israel, cleans them up, pours out his spirit or
active force upon them, and under the enthroned King Christ Jesus the
work is revived. (Matt. 25:40, 45; Rev. 1:7; 11:1-13) Their mourning
gives way to gladness.
Hence Zechariah 12:10 cannot be properly understood to support the
trinity doctrine.