Why is it that, when you start a Tumblr blog, the themes are in Latin?

Here is a succinct, well-worded explanation about what you saw --- Lorem ipsum ...

http://www.lipsum.com/

At that URL, there is even a button that you can click to generate a user-specifiable quantity of "Lorem ipsum" paragraphs.

For extra good times, you can generate a few "Lorem ipsum" paragraphs, copy/paste them to Google Translate ( http://translate.google.com/ ) in the first box, then choose to translate them into any of 80 different languages that are offered at Google Translate.

I've never had a Tumblr, so I wouldn't know whether or not they actually are Latin or if you're confusing some language with Latin, but my best guess would be:

Tumblr, being something on the internet and therefore worldwide, is accessible to people of many languages. Latin is a "dead language" that no one actively speaks, but is also the root language in almost all the languages we have today. So they probably use Latin so that they can use the same samples for everyone, regardless of language, and yet have it so that no one actually can read it (unless, of course, they've studied Latin). In other words, it's like having gibberish, except instead of straight gibberish, it has perfect grammar and a defined writing style, and that way, it looks more like an actual post rather than someone mashing a keyboard.

Yeah. That always freaks me out. The same happens in Wordpress theme examples.

I guess it's there purely for example.

And to show that no one knows Latin anymore.