The safest way is to install Dirty Swamp 3 into a "clean" Gothic II installation, in which no other modifications are installed. But in most cases there should be no problems if several modifications are installed in parallel.

1.: Gothic II Gold (Gothic II + Addon Night of the Raven)
2.: [url="https://www.worldofgothic.de/dl/download_278.htm"]Gothic 2.exe report Version[/url]

3a.: Install [url="https://forum.worldofplayers.de/forum/threads/1571097-Release-Gothic-½-Union-Ressourcen-Manager-(DEU-ENG-RUS)?p=26654299"]Union[/url] (including primary patch)

3b.: If you absolutely do not want to use Union [Union is the advancement of the SystemPack. We personally see no reason to use SystemPack instead of Union]:
3b 1: [url="https://www.worldofgothic.de/dl/download_168.htm"]gothic2_playerkit-2.6f[/url]
3b 2: Install the [url="https://forum.worldofplayers.de/forum/threads/1340357-Release-Gothic-½-—-SystemPack-(ENG-DEU)"]SystemPack[/url] instead of Union and [url="https://forum.worldofplayers.de/forum/threads/1530307-Hin-und-wieder-Abstürze-Renderer-Schuld?p=25974614&viewfull=1#post25974614"]4GB Patch[/url]
3b 3: Disable Data Execution Prevention for gothic2.exe:
Open Control Panel: System and Security: System: Advanced System Settings: Advanced: Advanced -> In the settings window:
Data Execution Prevention
Either enable the Data Execution Prevention only for required Windows programs and services or add Gothic2.exe as an exception.

4.: D3D11 Renderer: If the renderer is to be used, it should be installed BEFORE Dirty Swamp [url]https://forum.worldofplayers.de/forum/threads/1546222-Yet-Another-D3D11-Renderer[/url] [URL="https://github.com/Kirides/GD3D11/releases"]Kirides releases[/URL]

5.: Start Gothic II here once as a test to see if installation works so far.

6.: Install DirtySwamp-english-3.0.18.exe

download WoG:
[url]https://www.worldofgothic.de/dl/download_480.htm[/url]

8.: Start Gothic II\system\GothicStarter.exe and start Dirty Swamp with it

9.: If you are able to start a new game in Dirty Swamp without any problems, you can now install the recommended patches if you want (also pay attention to the requirements there!):

9.1.: [url="https://forum.worldofplayers.de/forum/threads/1547954-PATCH-BetterTorches-Fackeln-per-Tastendruck-ausrüsten-ablegen"]Better Torches[/url]
9.2.: [url="https://forum.worldofplayers.de/forum/threads/1546962-Patch-G2-Kategorisiertes-Inventar-Categorized-Inventory"]Categorized Inventory[/url]

(If you install the D3D11 renderer after installing Dirty Swamp, you should reinstall Dirty Swamp afterwards. Otherwise the game will start with wrong particle effect settings and some effects will be rendered completely wrong and the performance will be worse).