In Tolkien's texts, Sauron flees Dol Guldur just prior to the arrival of the White Council's force.
Galadriel is the Lady of Lothlorien, granddaughter of Finwe the High King of the Noldor and one of the last elves (perhaps the last) in Middle Earth to have seen the light of the Two Trees. She survived through incredibly dangerous and destructive periods of history and wields Nenya, the Ring of Water. She is the most powerful elf in Middle Earth.
Galadriel lived many years with Melian, and was instructed in powerful magical presumably. Couple that with Nenya and millennia worth of wisdom she would easily be the strongest non-maiar magician alive. Strong enough to banish(scare-off is more in line from text) a weakened Sauron certainly, and later she fended off the advances from Mordor during the war of the ring, which the films skip over.
Anyway, I think I know the part you're talking about.
"It has begun"
"The East will fall"
"So shall the Kingdom of Angmar rise"
Saruman lifts up his staff
"the time of the Elves is over"
"The Age of the Orc has come"
"You have no power here" etc.
The Black Speech was likely based entirely on Valarin, as Morgoth and his Maiar (all of whom would have spoken Valarin) minions did not possess the Secret Fire, but were only able to corrupt things to their service. It may have also been based on Quenya.
Tolkien describes the language as existing in two forms, the ancient "pure" forms used by Sauron himself, the Nazgûl, and the Olog-hai, and the more "debased" form used by the soldiery of the Barad-dûr at the end of the Third Age. The only example given of "pure" Black Speech is the inscription upon the One Ring:
Ash nazg durbatulûk, ash nazg gimbatul,
ash nazg thrakatulûk, agh burzum-ishi krimpatul.
When translated into English, these words form the lines:
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them.
Now, I found a website to translate Black Speech into English, and as you can imagine it takes a horrendously long time, but I had a crack at it.
Black speech: Shar gul
English: no sorcery
Black Speech: Fund mabas shatragtaum
English: Doom after disguise
Black speech: Goi rhothos ushtar
English: City besiege by army
As Lady Galadriel says “you are nameless, you are shapeless, you are formless etc”
I translated it as:
Black speech: Ragur
Black speech: Tanfuksham
I know this is no exact translation, but if you would like to have a go at translating yourself these are useful sites:
Black Speech Dictionary
English to Orcish Dictionary