The duplicate texts as in Kie_009 and Kie_009a are, as far as I can see, different texts on different situations in the game.
The missing [(indistinguishable)] texts can all still be added. Which texts are still hidden in other .uax files, I can't tell now. That would probably have to be controlled in the game.
The goal is to have the patch as complete as possible, as well as to reduce its size.

Ok, thanks, looking forward to the next version.

Most errors were fixed by StrangeAeons about 3 days ago. Just remember to redownload the file, I updated the file, but with the same download link.
The only thing left is subtitles flag to be set in CreaturesSFX file. There are few lines, but they are just transliterated fantasy language, so its not that important.
In other words, for subtitles to work you need to download 3 files :
System/Subtitles.int
Sounds/Voiceover.uax
Sounds/LevelMechanics.uax

Any version of the game will work with any mod.
Just remember, if you have non-English audio, voiceover file will overwrite it
Duplicated text is game behavior :
It has audio files with the same text in different tones, and names of the files are different (with a, b, c etc in the end) . I included all the files, so all the game audio files are subtitled

@StrangeAeonz & Vindoza: did you edit the .uax files yourself (if so, with which tool?) or took them from a mod?

"The only thing left is subtitles flag to be set in CreaturesSFX file. There are few lines, but they are just transliterated fantasy language, so its not that important."

Yes. This subs are for the Jemas in EternalAutumn.

I took the uax files from game versions that have translated subtitles and english audio.

I think StrangeAeonz took them from spanish version of the game

When I played the game, the lines: "It's a quaint little stage we all dance on." and
"But I've been waiting too long for this opportunity to be upstaged now." were missing during the Keisinger fight. Would somebody please test it? I think I have the latest version of the subtitles.int file. And as these lines are rather metaphorical, could somebody explain the exact meaning of "a quaint little stage we all dance on"?

I searched throught header of the original and subtitled uax file and couln'd find anything related.
I used this as the file format
https://bunnytrack.net/ut-package-format

So, header of the modified file
C1 83 2A 9E 55 00 00 00 01 00 00 00 6E 02 00 00
40 00 00 00 66 02 00 00 43 88 04 02 04 00 00 00
27 88 04 02 B9 BF C4 B8 69 40 6B 4A 8D 8E 60 F9
59 48 A9 F1 01 00 00 00 66 02 00 00 6E 02 00 00

Let's have a look, the first line grouped
[C1 83 2A 9E] [55 00 00 00] [01 00 00 00] [6E 02 00 00]
Here:
[C1 83 2A 9E] sign of the Unreal Music package
[55 00 00 00] version of the package (Undying had 55 verson)
[01 00 00 00] Package flag (0x01000000 is PKG_AllowDownload)
[6E 02 00 00] Name count

Second row
[40 00 00 00] - Name offset
[66 02 00 00] - Export count
[43 88 04 02] - Export offset
[04 00 00 00] - Import count

Third row
[27 88 04 02] - Import offset
[B9 BF C4 B8] [69 40 6B 4A] [8D 8E 60 F9] - part of the GUID

Forth row
[59 48 A9 F1] - part of the GUID, so the full GUID is [B9 BF C4 B8] [69 40 6B 4A] [8D 8E 60 F9] [59 48 A9 F1]
[01 00 00 00] - generation count
[66 02 00 00] - once again export count
[6E 02 00 00] - once again name count

If the get original file, the changes are:
row 3: [3F 88 04 02] - different export offset
row 4: [23 88 04 02] - different import offset
row 4 : [80 17 69 89 66 ED D4 11 A0 F1 00 C0] - different GUID
row 5: [4F A1 61 B3] - different GUID

-------------------------------------------------------

So the thing is the file is somehow different, that's why offsets are different (offset points to the end of the file).

After the header starts block of file names (they are in different order, but the format is the same for both files)
But the start of the RIFF WAVE block different by a few bytes. So I suggest maybe filenames were slightly changed in localization (maybe an error in one name). I need to export all WAVs and compare them
File names block, let's have a look at any one name
Liz_007:
original
08 4C 69 7A 5F 30 30 37 00 10 00 07 00
modified
08 4C 69 7A 5F 30 30 37 00 10 00 07 00

[08] - length of the name
[4C 69 7A 5F 30 30 37 00] is Liz_007
[10 00 07 00] Object flags, 10 00 07 00 is
RF_NeedLoad
RF_HighlightedName
RF_ErrorShutdown

So the name block is the same

Filenames are the same between two files just in different order. But I can't understand why the start of the RIFF is different

The wave files are the same. You can unpack them with dragonunpacker and compare them with winmerge.

Also, I took a brief look at Levelmechanics file. Both files are of the same size and I suggest offsets are the same. So the only change in header is GUID. So maybe they accidentally broke something unimportant in voiceover file (not necessarily cause anything wrong in game)
So I'll look closer into the bytes before RIFF flag. And the edning of the files with import and export tables

You've probably figured this by now, but just in case:
In the modified file Voiceover.uax, one of the filenames in the table is labelled "Voiceover_est", while in the original file it's called just "Voiceover". This should account for the 4 additional bytes in the part preceding the RIFF tag (and for the overall size being 4 bytes larger).

However, just by changing the GUID of the original file to the one of the modded (Spanish?) one does not result in showing subtitles. So the order of the files must also be important (?)
Edit: The GUID seems irrelevant, meaning that the subtitles will play whether the modded file has its own GUID or the original's GUID.

I compared Levelmechanics. Except the GUID everything is the same, offsets and so on. Bytes before the RIFF also the same. Names are in different order, but they are exactly the same, bit to bit. So the only thing that could be different is either bytes between the raw wavs (I'm not very experienced with this format, I suggest there aren't any flags inserted) or import/export table at the end of the file. Table is different between two files, but I didn't went through format specification yet. Unreal Viewers said that export pieces they see are the same, but I need to check it on hex level, not interpreted.

GoG user "surfer1260" made a massively scaled down patch for the subtitles from the existing data (thx). You are welcome to test it diligently to maybe find bugs---> https://www.mediafire.com/file/ejqsg8v5mdco74v/Undying+Subtitle-Patch.rar/file

My browser says "virus detected" and refuses the download the file. Sure it's safe?