Pseudo-Localization

Pseudo-Localization is a method used in software-development to show text/strings in ways to cover for different fonts/languages. Mainly to see live how different languages will be displayed in the user-interface, but it also has some other uses commonly related to translation and localization.

While this technically doesn't affect the average RimWorld player, there are reasons for the game to display some text as zalgo in specific situations. Since the question about what that means comes up often in the community, here's a quick explanation why it happens and other relevant info on the topic.

Most typically the text just means that whatever adds it (basegame, mod, etc.) is missing translations for a/your set language. It also only shows that way whenever your have dev-mode enabled in the game-settings. In Rimworld it's primarily a tool for developers to find (yet) untranslated text easily - that's why it only makes sense to show up in this case. But since having dev-mode ON in RimWorld can be quite useful for users and not just developers, you might sooner or later encounter some zalgo-text in your game.

Technically there's no further harm in having zalgo showing in your game - besides the text looking weird of course. If it annoys you that much though, you can simply turn OFF dev-mode and text should be shown correctly again. Optionally you can contact the mod-author about it, especially if you think it was an actual oversight and is not just some work-in-progress or temporarily missing translation.

Additionally there is at least one way to disable the feature even with dev-mode ON - simply by using Better Log, which has an option to disable that behaviour globally. It's also a quite handy mod you potentially want to have around in general - so it should be a no-brainer to use it that way.

If you're mod-developer and it's your own mod showing zalgo-text, you might want to read more about how to translate your mod on the respective Wiki article. And as usual; if you need more info or help with modding just in general, the mod-development channel on the RimWorld Community Discord is always there to give advice!