The file voc_ar.txt is based on the arabic vocabulary list in the snowball-data
repository: https://github.com/snowballstem/snowball-data.
Their file was produced from the "Arabic Wordlist for Spellchecking"
version 1.6, downloaded from: https://sourceforge.net/projects/arabic-wordlist/

The commands used to create voc.txt.gz were ("sort -u" used because there's one
duplicate word in the list):

unzip -p Arabic-Wordlist-1.6.zip Arabic-Wordlist-1.6/arabic-wordlist-1.6.txt|sort -u > voc.txt
gzip -9 voc.txt

The "Arabic Wordlist for Spellchecking" is licensed under the GPLv3+:

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