okay, let's play with the numbers.
1000 agents take 3 hours (each, I assume)='s 3000 hours
OR
10 agents 300 hours each ='s 3000 hours (7.5 weeks each)
Doesn't seem to daunting or unreasonable in the name of National security - and they had 4 years
But that's just the tapes, there's also those "millions of pages of other documents". Those too have to be translated and analyzed. Machine translation usually bites, but in this case it might help at least so that stuff could be "data mined" by computer, and then anything interesting that shows up manually translated.