As visible here and here, the episodes are listed in the correct order.

As visible here "https://en.wikipedia.org/wiki/Volcano_(South_Park)" ... Volcano (Knall endlich den Hasen ab!) was on air on August 20, 1997 so this is episode 2 "https://en.wikipedia.org/wiki/Weight_Gain_4000" (Wie werde ich ein Kampfkoloss) was on air on August 27, 1997 and is episode 3.

"https://www.southpark.de/seasons/south-park/yjy8n9/staffel-1" here is correct order.

So in the episode list must be an error...

And there is an error in the wiki articles, both episodes are marked as S01 E02...

But it makes no sense, earlier air on date should be Episode 2 ...

Taking in account that there are conflicting airdates available, we will need to find an official source.

If we refer to the US copyright records, Volcano is registered on August 20 and Weight Gain 4000 is registered on August 27, but these records are about the videocassette on which they are recorded and doesn't guarantee the real broadcast order.

This article from the night of the first episode also mentions Volcano airing the next week.
And I also found this long Twitter thread on this topic stating the same thing.

Thank you for your help, @Sheigutn . I have fixed the order.

Hello @superboy97 can you change the order please? Season 1 Episode 2 Weight Gain 4000 and Season 1 Episode 3 Volcano.

@soundeluxe said:

Season 1 Episode 2 Weight Gain 4000 and Season 1 Episode 3 Volcano.

As explained above, the correct order is the reverse.