I contacted the publisher on Facebook on another occasion and they seem to reply there, so maybe people want to ask there as well.

I don't have accounts on any Social Media platform otherwise I would ask there as well. Great suggestion btw.!

Meanwhile I received an answer from Assemble_Xer0 and this was his or her reply:

this is no problem at all.
Due to legal reasons, we cannot include Japanese and Chinese languages on GOG.
Those are limited and therefore exclusively available on Steam.

-cheers

So there is our answer, we will not receive the languages, case closed I guess.

I don't have enough time to contact the publisher and devs, but I checked some newer games published by Assemble Entertainment, and found that six out of eight games on the list are missing Japanese, and simplified Chinese if compared to Steam. :O

***I am the list***
1.ENCODYA
Missing Japanese, and simplified Chinese

2.Pizza Connection 3 - Languages
Missing Simplified Chinese

3.Endzone - A World Apart
Missing Japanese, and simplified Chinese

4.Leisure Suit Larry - Wet Dreams Dry Twice
Missing Simplified Chinese

5.Ultimate ADOM - Caverns of Chaos
All Good

6.Highrisers
All Good

7.Lacuna
Missing Japanese, and simplified Chinese

8.S.W.I.N.E. HD Remaster
Missing Simplified Chinese

List of games missing chinese: https://www.gog.com/forum/general_zh/index_63/post2

What the heck could be the legal reason for a missing language on GOG?!

Maybe it was a commissioned translation and who did the translation only allowed his/her work to be featured in specific platforms. Or maybe it was a completely unrelated reason, but I don't know what it could be.

Most likely it's about digital distribution rights and specific contracts between publisher, translation team and Steam as distribution platform. LLC has already published a small list of games missing some languages and I know there are others as well where german audio or subs aren't available. My guess is that GOG would have to negotiate for the rights to also publish the missing languages here.

This whole situation of missing languages so reminds me of the DVD/BD era and country codes. In this day and age this should be a thing of the past, sadly it isn't and will not go away or so it seems.
I was just asking in their Steam forums which really doesn't take much time. It's always a safe bet to receive a reply from a developer over there in a matter of minutes or the next day at the latest.

I once contacted a voice actor for work (not something I usually do at work) and they offered me a deal where we would pay them an amount of money for the voice acting and also a licensing fee for continued use of their voice work in the future. Basically we would've had to pay the voice actor a fixed amount of money for every year in which we used the audio files.

Like I said, I don't usually deal with voice actors in my line of work, but if this is the way these things usually work (maybe just in certain countries?), it's possible that some games on GOG lack certain languages because voice actors and/or translators in certain countries legally retain the rights to their work (voice files/text) and typically license them out for a set amount of time. I think we all know that some games even disappear entirely from stores if they contain licensed music for which the publisher no longer owns the license, so maybe the situation is similar here.

Coming from there, I don't find it hard to imagine that voice acting/translations might get licensed on a "per store" basis - which might lead some publishers to just decide they don't want to pay the fee for both Steam and GOG (and EGS and so on), so they just cut out those languages.

Wow, that's terrible. Imagine if movies did the same, we'd lose a bunch of classics due to expired music, dubbing, acting performance, etc..

Yeah, sadly.
But I already foresaw that streaming (which is fine just as an option) would have actually become a problem for availability and ownership :/

It gets worse. You don't just have to pay the rights holder for every language version, but you have to do so separatly in every country.

It's especially bad if you are a cultural minority. We are mostly german here in this region in northern Italy, it's hard to get any german streaming videos, since we can only make contracts with italian companies and they don't want to pay licence fees for a german version hardly anyone in Italy would watch.

In Europe it's tolerated, but not allowed to receive teresstrian TV and radio signals from foreign countries.
For cultural reasons we got a special solution which took a few decades to evolve. Some TV and Radio stations from Germany, Austria and Switzerland get patched to a local broadcasting station, a new logo gets mixed in, so legally it's a italian TV station broadcasting these programs and it costs us a shitload of tax money each year.

The european licence right system need an overhaul badly.

First of all: thank you all for the continous reporting of issues!

But please keep in mind that except for leaderboards, missing Galaxy features are not tracked here. For the time being at least.
Please report missing or broken achievements in the correct thread.

Also list should be up to date again!

Thanks a lot for updating the list and sorry for my share of inappropriate reporting.

Could someone clarify for me whether cloud saves and missing controller support are tracked on this list (once again thinking of Chernobylite here)? I'm assuming cloud support is not, since it only affects Galaxy users, but surely missing controller support is missing content, similar to missing language options, isn't it?