Translation:One coffee and a little cream, please.
I think it's fine for a lot of liquids. For example, "That salad dressing would be nice with a bit of lemon juice in it" or "This paint is almost the right color, it needs just a bit of red". English does not always preserve the semantics of bulk terms. For example, I just referred to a "lot" of liquids, which does not make sense etymologically but which you probably didn't even notice.
Just because you are the mod here and you've seen it in a (one) dictionary somewhere doesn't mean it's the most logical translation. Consider this:
In English we use "thank you" following a request to show gratitude. It's normal. There is no please in Finnish, so naturally, Finns don't have the concept for the word in their language to start with because it doesn't exist. It's a cultural expression unique to the languages that have it. But saying "thank you" is more universal. Finns don't have a concept for please culturally. Just ask a group of Finns and I guarantee that 9 out of ten will tell you there is no exact translation for please but there is one for "thank you" and because we also say "thank you" in English following a request, common sense (and occum's razor even) should tell you that it's showing gratitude, just as we do in English following a request.
My view on the matter is not based on my moderator status or any single dictionary, but rather my education and experiences in relation to the usage of the English language. The concept of "please" in this context is that it adds politeness to a request, and there are several ways of doing that, like inserting "kiitos" into it or starting the request with "voisitko". Translation doesn't always have to strictly follow semantic meanings of individual words, which can in fact be detrimental to the quality of the translation. When a child who is still learning the ropes of social etiquette makes what is perceived to be a too direct request, I have the feeling that you're much more likely to hear an adult say "say 'please'" rather than "say 'thank you'". One might say the latter if the child just received a gift or a favour. A Finn would be inclined to say "kiitos" either way, which doesn't make either word untranslatable. They can just translate to the same word in certain contexts. This isn't to say that the usage of "thank you" in the way you describe is incorrect, just that from my perspective it seems at least as common and probably more so to use "please" instead of "thank you" in this context in the Anglophone world generally speaking.
Native English speaker here. I would actually prefer "coffee and cream" to "coffee with cream". The latter sounds like I am asking the waiter to serve me the coffee with the cream already in it (which they generally don't do, at least here in California, unless it's a pre-made latte or something), whereas the former sounds like I am just asking for both items independently and I'll put in as much (if any) as I want.