2018-07-13 Updated Solution
Though this an old question, it and its answers provided the clues necessary for me to enable CUPS printing from a 64-bit OS via WiFi to a Brother MFC-J870DW.
The 32-bit support libraries necessary to run the 32-bit Brother drivers on a 64-bit Debian-based system have been changed, so the files referred to in the question and James Fu and Larry Wilson's answers are no longer in the repository.
The following steps got me to the correct libraries and successful printing...
First, try to install the meta package which will fail but will list the current libraries that replace it. Doing this first may get you the then-current library names if they change again in the future..
root@LX02:/# apt-get install ia32-libs
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package ia32-libs is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
lib32z1 lib32ncurses5
Now install those two libraries...
root@LX02:/home/alpha# apt-get install lib32z1 lib32ncurses5
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
lib32tinfo5 libc6-i386
The following NEW packages will be installed:
lib32ncurses5 lib32tinfo5 lib32z1 libc6-i386
0 upgraded, 4 newly installed, 0 to remove and 0 not upgraded.
Need to get 3,084 kB of archives.
After this operation, 12.4 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://ftp.us.debian.org/debian stretch/main amd64 libc6-i386 amd64 2.24-11+deb9u3 [2,597 kB]
Get:2 http://ftp.us.debian.org/debian stretch/main amd64 lib32tinfo5 amd64 6.0+20161126-1+deb9u2 [299 kB]
Get:3 http://ftp.us.debian.org/debian stretch/main amd64 lib32ncurses5 amd64 6.0+20161126-1+deb9u2 [99.4 kB]
Get:4 http://ftp.us.debian.org/debian stretch/main amd64 lib32z1 amd64 1:1.2.8.dfsg-5 [88.6 kB]
Fetched 3,084 kB in 0s (4,391 kB/s)
Selecting previously unselected package libc6-i386.
(Reading database ... 123518 files and directories currently installed.)
Preparing to unpack .../libc6-i386_2.24-11+deb9u3_amd64.deb ...
Unpacking libc6-i386 (2.24-11+deb9u3) ...
Selecting previously unselected package lib32tinfo5.
Preparing to unpack .../lib32tinfo5_6.0+20161126-1+deb9u2_amd64.deb ...
Unpacking lib32tinfo5 (6.0+20161126-1+deb9u2) ...
Selecting previously unselected package lib32ncurses5.
Preparing to unpack .../lib32ncurses5_6.0+20161126-1+deb9u2_amd64.deb ...
Unpacking lib32ncurses5 (6.0+20161126-1+deb9u2) ...
Selecting previously unselected package lib32z1.
Preparing to unpack .../lib32z1_1%3a1.2.8.dfsg-5_amd64.deb ...
Unpacking lib32z1 (1:1.2.8.dfsg-5) ...
Setting up libc6-i386 (2.24-11+deb9u3) ...
Processing triggers for libc-bin (2.24-11+deb9u3) ...
Setting up lib32z1 (1:1.2.8.dfsg-5) ...
Setting up lib32tinfo5 (6.0+20161126-1+deb9u2) ...
Setting up lib32ncurses5 (6.0+20161126-1+deb9u2) ...
Processing triggers for libc-bin (2.24-11+deb9u3) ...
Now use the CUPS management utility to setup the printer as usual. For newbies, unlike most other setup wizards, the cupsd
daemon runs a small local webserver and the wizard is implemented as a series of web pages. To start it...
As root
... start your browser and point it to local port 631. For example...
firefox localhost:631
The rest of the setup is outside the scope of this question.