/usr/share/myspell/dicts/th_pl_PL_v2.idx is in mythes-pl 1.5-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/myspell/dicts/../../mythes/th_pl_PL_v2.idx
/usr/share/myspell/dicts/../../mythes/th_pl_PL_v2.idx