BUG #17356: hunspell-hu dictionary processing error

The following bug has been logged on the website:

Bug reference:      17356
Logged by:          László Zsolt Nagy
Email address:      nagylzs@gmail.com
PostgreSQL version: 14.1
Operating system:   Debian Linux
Description:

How to reproduce:

# Start minimal virgin system
docker run -it --rm debian bash
apt update
apt install -y acl ca-certificates curl gzip libbsd0 libbz2-1.0 libc6
libedit2 libffi7 libnettle8 libicu67 libreadline8 libgcc1 libgmp10
libgnutls30 libhogweed6  libidn2-0 libldap-2.4-2 liblz4-1 liblzma5
libncurses6  libp11-kit0 libpcre3  libsasl2-2 libsqlite3-0 libssl1.1
libstdc++6 libtasn1-6 libtinfo6 libunistring2 libuuid1 libxml2 libxslt1.1
libzstd1 locales procps tar zlib1g gnupg dumb-init curl

# Install hunspell-hu and PostgreSQL
apt install -y hunspell hunspell-hu
curl -s
https://salsa.debian.org/postgresql/postgresql-common/raw/master/pgdg/apt.postgresql.org.sh
| bash
apt update
apt install -y postgresql-14

The above procedure gives this error during the last step:

Building PostgreSQL dictionaries from installed myspell/hunspell
packages...
  hu_hu
iconv: illegal input sequence at position 131
ERROR: Conversion of /usr/share/hunspell/hu_HU.aff failed

It happens when pg_updatedicts is executed.

I'm not sure where the problem is. It may be in hunspell, or hunspell-hu, or
iconv or postgresql. I have tried to find the root cause, but I falied. At
least it seems that it is NOT a bug in hunspell or hunspell-hu, because the
author of hunspell wrote this comment in 2018 at
https://github.com/hunspell/hunspell/issues/559#issuecomment-446335091 

> Not a bug: Hunspell's file format is not an UTF-8 encoded text file in the
case of SET UTF-8 with the default 8-bit FLAG.

That hunspell issue is only open because "it is a valid request", but it is
not a bug nonetheless (according to the author).

So it might be iconv, or it might be pg_updatedicts that calls iconv with
the wrong parameters. I do not know enough to tell...

I think that this bug has been around for years now, and it makes impossible
to use tsearch2 with Hungarian spelling.