/usr/share/myspell/dicts/th.aff is in myspell-th 1:4.2.1-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/myspell/dicts/../../hunspell/th.aff
/usr/share/myspell/dicts/../../hunspell/th.aff