To download a file (including a ZIP file), right-click the link, then "Save As".
To unzip a .ZIP or .7Z file on Windows, you can try 7-zip.
3.1) Start mkvinfo-gui.exe (coming with MKVToolNix), and open the MKV file in question (e.g. Gyu ep.1). I'll call it aaa.mkv.
Find the "subtitles" track, and check its Track number. If it says "track ID for mkvmerge & mkvextract: 2", the track ID is "2". You'll use this number later.
3.2) Start cmd.exe by hitting [Win]+[R] and then type "cmd.exe", then hit [Enter].
(If you're new to cmd.exe, first do some research and learn what "path" is and how to use "cd".)
To get an ASS file from aaa.mkv, type this simple command (in cmd.exe) and hit [Enter]:
mkvextract tracks "aaa.mkv" 2:bbb.assmkvextract is the path to mkvextract.exe (coming with MKVToolNix). aaa.mkv is the path to the MKV file (input). bbb.ass is the ASS file you're getting (output; a new file). 2: is the track ID (see above).
3.3) When you are done, type "exit" then hit [Enter] to close cmd.exe.
(3) may feel confusing at first, but actually it's not that difficult.
Once you learn how to do this, you can get an ASS file from an MKV file.
You'll then re-translate that ASS file into your language, and then you can use mkvtoolnix-gui (coming with MKVToolNix) to make a new MKV file, which has the original video/audio + your new ASS file.
In short, you can make a new MKV file on your own (which you can share with your friends), without downloading anything new (except the original MKV file itself).