> How many people use Gmail in a language other than US English?

You'd be surprised. There are only about 400 million native English speakers [0], and Gmail has 1.5 billion users [1].

If we assumed that all native English speakers use Gmail, they'd represent not even a third of the users. Of course, there are many non-native English speakers, but I'd assume a significant fraction of them would prefer to use Gmail in their language.

I'd argue i18n has a huge impact, but Google really doesn't optimize for it.

[0]: https://en.wikipedia.org/wiki/English_language [1]: https://www.cnbc.com/2019/10/26/gmail-dominates-consumer-ema...

I think the person you're responding to is agreeing with you that you should optimize for languages other than English rather than for people naming a label "Bin" and then switching to the UK locale.

But how many of those "users" are actually unique?

I, personally, have 3 "GMail" accounts: one @gmail.com, one @ my own domain, and one for work. So if I were the average English-speaking user of GMail, having every English speaker be a user would pretty much cover the 1.5 billion.

(I do not, in any way, think I am the average—I merely seek to point out that it's significantly more complicated to calculate than your post suggests.)

> There are only about 400 million native English speakers [0], and Gmail has 1.5 billion users [1].

Don't assume that only native English speakers (want to) use things in English.

The real question is how many people use advanced searching. I would guess the answer is < 1%.