It is a bit faster, was necessary for older Koreader version, but nowadays isn't. The dict-file can be zipped with dictzip* to dict.dz-file. (See
line 1333 of PocketBookDic.pl.)
I've
reupped the Oxford 2nd Ed with compressed dict.dz-file. It easier to decompress than to compress.

The script also removed all the nested blockquotes, that needed extra styling in Koreader.
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* Under linux it is a package, under windows you can use
this.