Earlier quoted context omitted.
A progress meter may not be necessary, but as the article points out if you have comments or an otherwise large footer not associated with the content of the post, the scrollbar can be deceiving. I'm personally a huge fan of the progress meter (having once thought it was redundant as well) - one other easy addition I didn't see mentioned is an "estimated reading time." Having a ballpark range for how long I should ex…
I'm not sure how "estimated reading time" works for non-english speakers. As for "progress meter" being an optimization of websites with large footers or long lists of comments, I'd argue that a better optimization technique would be to remove the footer, or remove/hide by default list of comments (i.e. make it available with a mouse click somewhere).
Do you mean people whose native language is not English? I assume it works the same way as for everyone else, i.e. it's always an approximation anyway. I'm not from an English-speaking country, but I'm pretty sure I read faster than the average English native.
The other interpretation is that you mean people who can't read English at all, but in this case I understand even less. They won't be able to read the article, if they don't speak the language. After automated translation, the reading time should be roughly correct again.