The article is always that of the container.
Eine/Die Schachtel Salz
Eine/Die Flasche Wein
The containers are countable, so if you've got multiple containers containing anything, the article is the plural form of the containers article
Viele Flaschen Wein
If you want to point at a certain set of bottles containing wine, you would probably use the ...
I don't know why there are plural forms for uncountable nouns like
Champagner, Sojasoße, Schokolade
Because you can still talk about salts, waters, or the various brands of champagne or chocolate:
Ich mag Schokoladen mit hohem Kakaogehalt. Chemiker interessieren sich für die Salze der Schwefelsäure. In Deutschland werden vor allem halbtrockene Sekte (non-...
Duden will tell you, in the »Bedeutungen« section,
Grammatik: ohne Plural
But only in some cases (most of Glück, some of Zucker, none of Milch).
Towards the end of the article there is a separate »Grammatik« section which will nearly always list a plural because there is some special case in which a usually uncountable noun will have a plural:
Glück: die ...
What you are referring to, is the decision, whether something is a singularetantum.
While in principle I see no difference to English, you have to look it up.
This property is a convention, which sometimes changes over times. The example Information is an interesting one, since it can be a unit (so you may just have little or much of it; one would measure ...
In almost all cases the German article for plural forms is "die".
Combined nouns always use the article of the last part of the combination.
Another example was "chocolate":
plural of countable form: