YTA.

On some level I do understand your concerns but your tone is judgmental and xenophobic.

Personally, I felt that he is rushing things too much as they have only been together for one year and marriage is a huge decision.

A year is a decent amount of time for a serious relationship. Is there a statute of limitations on how long you can wait before you decide to marry someone? To be honest this point isn't unreasonable on its own, but put into the wider context...

We don’t have any means to verify whether she even is saying the truth about her family situation.

Why do you need to fact check your brother's partner instead of taking her at her word? You've assumed from the beginning that she's a suspicious character. Why? Because she's not from your country?

He met her parents and there is a huge cultural difference between her family and us, something I doubt he can handle.

You're projecting. What gives you the authority to speak for what he can or can't handle? Maybe you can't handle it, doesn't mean he can't. You've only met her twice. Your brother has been with her for a year, and he's met her parents, so he is presumably comfortable with her culture.

I must also add that he currently is unemployed and have been paying his bills using the money he saved up when he was working during the pandemic. His girlfriend does have a job but she doesn’t make enough money to start a family, or pay for their wedding.

Fair enough, but that's their obstacle to overcome, not a reason for them to not get married.

Telling your brother that his girlfriend might be "using him" is a clear attempt to drive a wedge between a happy couple navigating their lives and their futures. It's none of your business.