Old(er) men creeping on young women [at work]

Your OP was absolutely fine because all the details show the power imbalance in play.

Well done for stepping in, you did the right thing.

The age or nationality of either party is irrelevant.

Sexual harassment of all and any woman by men needs to stop.

Yes, I would have intervened and said to the woman, oh is this your dad?

I will always intervene if I think someone is being made uncomfortable. I'm not the most subtle sometimes but I'm still standing to tell the tale (just).

I have seen worse, to English girls, just from the age of 17 to 19. Worked in a cafe once and one 80 year old proposed to be a sugar daddy to one of my youngsters, described his offer in its entirety, to visit her in her uni city, to buy her a small car and other things in return for something. It was totally crazy. The man looked about 80, and the way she described how he spoke to her, could not be a joke. Who is this normal man to harass sexually ( even though verbally ) a 18 year old as a joke...she said he also was repeatedly looking her up and down multiple times

I don't need to describe myself as anything. I very rarely get asked where I am from and I certainly wouldn't expect people to refer to me as immigrant, non-english or whatever. I trust that people who make my acquaintance will simply say "I met a woman the other day" and don't feel compelled to infer that "my culture" is somehow different from theirs and make it my defining feature.
In your shoes, I would have probably come up with a random thing I "needed help with" so as not to make the woman more uncomfortable than she needed to be and also to give her an opportunity to go back to the conversation with the bloke if she indeed wanted to. But it's hard to say as I was not there and I can only judge what happened by your (wildly improbable) story.

This feels very disingenuous. Anyone, anywhere, in a land that isn’t their native territory will be more cautious and more facilitating. In an attempt to be open to other cultures, a “benefit of the doubt” mindset tends to rule- which in this case could well have been “this feels creepy but maybe this is normal cause no one is objecting, and I don’t want to cause a fuss so I’ll just tolerate it.”

Cultural rules, norms and mores aren’t written anywhere- you are always playing a guessing game. I still remember to this day landing at Heathrow, and riding the Piccadilly line to “Cockfosters” and laughing out loud at the name (yes I know it was juvenile) and smiling at the person in the carriage opposite me. It wasn’t until later that I recounted to someone the alarmed and hostile look I received when they explained “don’t make eye contact with people on the tube.” It’s not about “forriners” being weak or dependent, but having a natural disadvantage due to navigating unknown territory! How the hell do you know not to make eye contact on the tube? THERE SHOULD BE SIGNS.

And indeed we knew that there were other women on their own in that part of the shop that day - he targeted a young foreigner, the disgusting pervert.

Maybe she felt it relevant as I often see non native speakers as being more vulnerable, so felt for her even more.

I stepped in on a bus when a young female Chinese student was being harassed by a large drunken man. I could see she was turned away from him tight up against the window and he kept shifting closer, pushing his leg against her. After I intervened, he got up left the bus. The non-native issue was also present in this case - she was trying not to offend but obviously did not know how to handle it. So,well done OP.

Isn't it obvious to you? Surely , you're not that naive?

I was perfectly capable living in another country at 18 - but I have no difficulty in understanding that many other women would feel more vulnerable in a country where the language is not their first.

No assumption - that was what we were told by her tutor.

You can disagree. But again, your store manager made an assumption since none of you actually spoke to this women. As a "non-english" I can assure you we are perfectly capable and don't need patronising by the "natives".

No, I disagree. I think it is an even bigger issue when the woman is not local. I took a phone call years ago working in retail from a university tutor reporting an unpleasant incident her student newly arrived from abroad had had in our shop. We were all shocked and the store manager commented on how awful it was that she had felt so uncertain and nervous that she hadn’t asked for help from any of the staff.

You did the right thing op.

Would you have said anything loudly so the man could overhear?

Only if I was prepared to have my lights punched out.

I would feel that if my own dd moved abroad and had limited language in that country, that she would be even more vulnerable than a native young woman.

OP you did exactly the right thing!