[masaegu]

I think I've got it. At least it appears to make sense in the sentence.

万籟闃(ばんらいげき)として = "in complete silence"

And to answer my own question, I think the phrase 「協力一致によって独乙の自由へ」 was in a European language, mostly likely none other than German, which would require one to translate the 大文字 as "capital letters".