THQ made it possible recently. On Steam version at least.
I know it's possible with mods but still would like to play things without them...

This solution has been subsequently identified as just a long-existing mod that strips all the addon content from the Gothic II Gold Edition, it's not actual Gothic II Classic.

The only place you can still get Gothic II Classic from is actually GoG. Or used to be, at least.
You would ask GoG support for the Gothic II Classic offline installer, and, if you actually owned a copy of Gothic II Gold Edition on GoG, they then would provide you with a link you could download a 2GB offline installer (setup_gothic_2_gold_edition.exe) from.
The major downside being that it's the international version (v1.32), with the sometimes hilariously, but most of the times horrendously terribad English localisation.


Guide to patch Gothic 2 Gold Edition back to original, expansion-less Gothic 2 (via the WorldofGothic subreddit):

The original instructions come from the Gothicz.net forum by Milhaus and has since been edited by u/auronen and u/nr3jokim

Note: Do not install Union or any other patches until instructions mention it.

This guide is only applicable for GER and ENG languages right now. Polish version will be supplied as soon as possible.

1. Install Gothic 2: Night of the Raven in either English or German version
a) GOG: Either contact GOG support and get original G2 Vanilla installer (and skip all of this to step 7), or install it via their G2:NOTR installer
b) From CD: Install it from CD via its installer, nothing special

2. For language selection, pick the correct GOG installer option. Select any language you want, but the rest of the guide sets everything to German language, except for the voice acting. So if you want Polish voice acting, select a polish language. As for the text translation, that is covered in step 8.

3. Download and copy this to the System directory in the game and rewrite the original file.

4. Download and install (be sure to pick the correct game folder) this

5. Download and install (be sure to pick the correct game folder) this → pick gothic2_fix-1.30.0.0.exe

6. You need to disable all VDF archives in Gothic2/Data that include NOTR assets. We need to rename all VDF files containing Addon in its name. The game checks files for its file extension, so we will rename all affected files to file.vdf.disabled, such as example: Gothic2_Addon_Weapons.VDF rename to Gothic2_Addon_Weapons.VDF.disabled

7. Now we need to manually install Union. We need to install both Primary Patch and Union itself. Primary patch is really important as it fixes the music. You can find both Primary Patch and Union here. If installer asks, we are installing Gothic 2 Classic

8. If you want to play in English, you will notice that dubbing stayed in ENG, but all the text is in German. You can fix that by copying this to the /Data/ folder in your Gothic II root folder. We are currently searching for the Polish vdf, but your only choices right now are now German (don't change anything), or English (use the VDF sent above).

9. You can now install other language patches and other mods, if you know some.

10. Start the game with Gothic.exe, not GothicStarter.exe