"This is a good meal."

Translation: To jest dobry posiłek.

[TatianaJac]

Why not Ten jest dobry posiłek?

[Jellei]

Because "this" is not used as a pronoun here (this dog, this man, this bottle), but as a subject (This IS). And the sentences of "This is/These are" model always require 'to' which is then not a neuter pronoun but the subject as well: To jest/To są.

[Marge180616]

Why can't I say "to jest dobre jedzenie"?

[Jellei]

While the meaning may be close, "jedzenie" is "food", so it's not exactly the same as "meal".

[NJG88]

What's the grammatical reason that "dobry posiłek" isn't in the instrumental here?
I thought there was no predicate nominative in Polish?

[Vengir]

To put it simply, sentences that would translate to English as "this is…" use nominative.

[Peter800730]

Why not pośiłek (I hear an accent on the s). This just seems to be wrong.

[alik1989]

It's a very practical spelling convention. Since si is always pronounced "śi", the diacritical mark is omitted. It's a mistake not to omit it. Same goes for ci and zi.

[AlT2rD]

What's the rule(s) for dobra / dobre / dobry?

[Jellei]

"dobra" is feminine singular, "dobre" is either neuter singular or 'not masculine-personal plural' (non-virile), "dobry" is masculine singular. They have to match the noun they refer to.