GOG provides:
13a4c613edc23df50f23c00142744978 Warrior Kings Battles - Manual.pdf

Another one is not included.

I'm back after a (much needed, as it turns out, as the last 6 months were quite stressful for me) 6+ month leave from gaming and forum-frequenting. Good thing that ZFR, Grargar and the others were around and kept stuff in the thread updated.

I added the changes from June (when I stopped updating the gogmix due to my leave) till now, and also found out a couple of new things.

First, the manuals for Titanic: Adventure out of Time. As I state in the gogmix, I found a bad quality english manual at https://www.myabandonware.com/media/files/manuals/t/titanic-adventure-out-of-time_windows_0iyr-manual.pdf and a french manual with better quality at https://www.abandonware-france.org/ltf_manuels/manuels.php?id_manuel=810.

It also appears that the img.metaboli.fr links are currently dead. It seems from the thread that at least some of them were live at least on the 18th of December (given that ZFR posted one such link), but I have no idea whether they'll be alive again or not. The most important manuals I drew from those links were the Gray Matter ones, and admittedly I panicked a little bit when I saw that those links were dead. Then I remembered that I might have saved them in one of my external hard drives, and indeed I found them there, alongside the downloaded gog installer files. These manuals (english and french) can now be found at a folder on my Google Drive, at https://drive.google.com/open?id=1ziTIOQYPCPPcHc0jF1HgY-_a2D4LTdlE.
In regards to Gray Matter, another interesting thing I found out is that a Spanish(!) manual is located in the install folder - I updated the gogmix accordingly, adding this information.
The other manuals affected were the French manual of Sherlock Holmes: The Awakened, the Gold version of Serious Sam the Second Encounter and the manual of the Immortal Throne expansion of Titan Quest. I found the latter at replacement docs (but it is probably of less good quality than the one from metaboli I initially linked, otherwise I would have linked this one from the get-go instead), but I haven't found the others so far, so I'll have to remove them from my gogmix if their links continue to be dead.

That's all for now. Admittedly, I'm not sure whether I'll keep updating the gogmix on a regular basis or not (things might get stressful again sooner or later), but I might try to at least let people know (via the gogmix and/or the forum) if I happen to find a manual link not found by others.

English manual:

Railway Empire

Thank you. I will update soon.

Update: I found manuals for Dungeons 3, Crookz: The Big Heist and Urban Empire and modified the links for Railway Empire, Tropico 5 and Dungeons 2 to add more languages. The parent website of these manuals http://www.download.kalypsomedia.com/manuals also has many other manuals, but those were either for games which already had at least 1 manual or aren't on gog at all.

Thanks.

GOG provides manual now.
dungeons_2_manual.zip
c1e133171ef4fe8af6efaf5861f31ef7 Dungeons 2 - Manual.pdf

Dungeons 3 also seems to have a manual now, according to the store page. I'll remove these 2 then from my gogmix but will paste their text here, because it mentions the location of the other language versions of them:

Dungeons 2
The manual can be found here: http://www.download.kalypsomedia.com/manuals/D2_PC_UK_MANUAL_ONLINE.pdf Other languages: Substitute the UK in the url with DE, ES, FR-IT (which leads to a bilingual French and Italian manual), RUS.

Dungeons 3
The manual is at http://www.download.kalypsomedia.com/manuals/Dungeons3_Manual_PC_UK_ONLINE.pdf. For other languages, replace the UK part of the url with FR, IT, DE, ES.

^ There's an error in one of your links. Full Throttle Remastered points to Grim Fandango.

Removed. Thanks.
Added. Thanks.
Corrected. Thanks.

All updated now thanks.

The list should be up to date as of now. If you find any more changes that have to be made, please let me know.

Vikings: Wolves of Midgard
Vikings Artbook
Vikings Soundtrack

Just added to my gogmix the manuals for the newly released Warhammer 40.000 Armageddon and Warhammer 40.000 Sanctus Reach.

Thank you.
However after thinking it through, I've decided to only include here manuals, reference cards or similar. Other extras might cause the list to grow out of proportion.

Thanks anyway.

EDIT: However I did notice that the game now contains a manual. Going to remove from my list.

Added.

Also, check note above. VIkings: Wolves of Midgard seems to have its manual included now on the game page. You might want to remove if from the gogmix.