W zdaniu "The film is available for workers for whom English is a native language" przedimek "the" przed workers jest zbędny? Bo zastanawiam się czy pracownicy w tym przypadku nie są konkretni - ci, dla których angielski jest rodzimym językiem, "the workers"
"Concrete" is a useful word, but forget the adjective "concrete" as you use it in this sense.
Bear with me:
One could as well say "…for those workers for whom English is…"
"…those workers for whom…" would clearly be definite and equivalent in terms of (in)definiteness to "…the workers for whom…" As definite, "those workers" would require the definite article sans the demonstrative "those."
…byc moze wiesz, ilu ich jest w tej chwili, ale potem przyjda nowi. Wszystkich nie wyliczysz.
What mg said is nonsense: the definite article before a plural countable noun is "inclusive of its membership" for entirely different reasons. It doesn't require of you to know their numbers, identities, or home addresses.
I will let you in on a secret: the definiteness of a plural definite is "inclusive" by way of its power to delimit. Its "inclusiveness" with no additional modification implies (but doesn't state overtly) its domain-universal truth:
I can say, "All the workers deserve a raise except mg." Note the additional modification that "all" delivers.
But I cannot say, "The workers deserve a raise except mg."
The indefinite countable plurals characterize the members of a type, whereas the definite plurals delimit the membership in a set named by its type or points to a new subset so defined.