Sizes in women's clothing

I've been getting a slightly strange reaction in Berlin shops when I go shopping. I'm 5 foot 9 and I wear a size 6 in the US and a size 10 in the UK. In clothes that come in Small, Medium or Large, I tend to fit best into a Medium or Small.

When I go shopping here in Germany and pick up my usual size (which is a Medium or the equivalent of a US size 6) I find that sales assistants say, "Oh no! You need a Large" and shove a Large at me. I picked up a denim skirt to try on the other day in a size Medium and the sales assistant said, "what size do you have there? That's very very small. I doubt that's gonna fit you." and then she handed me a Large and an Extra Large!

The weird part is that all these Large sizes they hand me just fall off me and I always end up buying a Small or Medium since those are the sizes that fit me.

Is it that the sales assistants here see a tall woman and automatically equate that with being "Large"?

I've never heard of that here, I've had the same in Russia but not in Germany!

I'd say if you're a UK size 10 then most probably a small would be the usual equivalent however because you're tall then yeh a medium. I'd have said a German large was equivalent to a UK size 16 or a 14 at the least- Personally I wouldn't expect it to equate to less than that.

Shame they don't have a 'tall' range here like in the UK.

A 'large' size in German terms would be a European size 46-48 which in turn is about a size 16-18 in the UK and a 14-16 in the US...
A UK size 10 is a 38 here so kind of a small/medium

It very much depends on the store you shop at. If they are stores like H&M or C&A Clockhouse or something, then the sized tend to be smaller, i.e. a Large there might be like a medium at other stores.
But I don't really go by sizes anyway, I just try what looks like it could fit, and if it does it does.
A US size 6 would convert to a 36 here which is a small, or maybe a medium sometimes (because of your height).