Here in the Northeast of England (and in some other British dialects), it's common to hear phrases like ten year or twenty pound, with nouns quantified by a numeral lacking the plural morpheme you'd find in Standard English. It's one of the features of the Geordie dialect I quite like, though I don't do it myself. (Although you'll notice that the colloquial terms quid, nicker and so on tend to be singular - you don't ask someone to lend you twenty quids or twenty nickers. In fact, you'd get some decidedly funny looks if you did ask for that, and possibly a bumper pack of underwear.)
Andrew Graham Dixon presented a Culture Show special called Cash in China's Attic on Friday night, about the booming antiques market in China. He kept on telling us the price of various things, and sometimes he said It's thirty thousand Hong Kong dollars, but sometimes he said It's thirty thousand Hong Kong dollar. He seemed to alternate between using the plural and singular forms. He's not a Geordie, or a speaker of any dialect that this is a feature of, as far as I know. And it's not the case that dollar is always used in the singular in this currency, and he was experiencing L1 influence from English: a Chinese man used the plural form.
What I think was going on is that he had an interesting case of assimilation to the dialect of many of the people he would have met in Hong Kong. Chinese (Cantonese or any of its other varieties) doesn't have much in the way of inflection, and it doesn't have plural morphology. This means that, although people from Hong Kong mostly seem to speak excellent English, they sometimes make mistakes like not using plural forms. So a lot of antiques dealers and shopkeepers probably told Andrew Graham Dixon the price of things by saying It's one thousand dollar. Either he's just got used to it and started saying it the way everyone else does, or he's assumed that that's the way it's meant to be said and done it consciously. I don't know which, but it sounded decidedly odd.