This question is a bit opinion based, so what follows is just my opinion.
I think the declaration of human rights would be OK for testing out a few lines of text for font samples. I don't think you need every single glyph or letter in such a sample. You are not limited to this however. If you don't just want to copy google's approach, there are other samples of text you could use. Maybe the works of Shakespeare, or maybe even other quotes from famous writers, etc.
However, I'd personally rather use Lorem Ipsum for layout purposes, like for generating whole paragraphs/pages of text. These use cases aren't really the same. They perform different functions.
What's good about Lorem Ipsum is that it can be used to make blocks of text. It's genericness is useful. It's just text. It has no specific meaning. There's no formatting. There are no numbers or weird glyphs. It looks like normal paragraphs of text, like you'd find in a book, or magazine.
I wouldn't use the declaration of human rights for layout, or quotes from real books/authors. The problem is that these already have a layout, specific paragraphs, and formatting, maybe even numbers, or lists. This kind of text is just too specific, and not generic enough. So, it won't work well for blocks or paragraphs or full pages of generic text for layout purposes when all you really need is unformatted filler text that is devoid of any actual meaning.
Also worth pointing out that most people already know that Lorem Ipsum is filler text. If you use actual text with meaning, you might have to explain that the text is only being used as a filler or place-holder. Also, the content itself could be distracting.