This is a tough one. Many English words can be both (beer, time, glass, language, etc etc) depending on the context/meaning.
Figuring out (un)countability from the word alone or from a regular dictionary is impossible or impractical.
You can try to figure it out from a large text corpus by seeing how the word is used:
- if there's a plural form or not
- if there's an indefinite article before it or none
- if it's used with many/few, much/little, a piece of(?), etc
But many words can function as both nouns and adjectives and that complicates matters. For example in an air pump
, air
functions as an adjective and an
refers to pump
, not to air
.
Likewise, many words can function as both nouns and verbs and have identical forms. For example, in she pressures him
, pressures
isn't a plural of pressure
.
Also, some uncountable nouns can have an indefinite article before them when they are made more specific, e.g. knowledge
vs a good practical knowledge
.
You can gather statistics from an analyzed corpus and based on it judge whether or not a word is more likely to be countable or uncountable.