Vinum acre hospiti non placet.

Because placeo, placere works differently from English to like.

In Latin, placet literally means is pleasing. So instead of saying:

• The guest does not like the wine

Latin says something more like:

• The wine is not pleasing to the guest

That is why:

• vinum acre = the thing that is pleasing/not pleasing, so it is the subject
• hospiti = to the guest, so it is in the dative

This is a very common pattern with placeo.

By the grammar of the whole sentence.

Vinum is a neuter second-declension noun, and its nominative singular and accusative singular forms are the same. So by itself, vinum could be either one.

But here it must be nominative singular, because with placet the thing that pleases is the subject:

• Vinum acre ... placet = The bitter/sharp wine ... pleases
• hospiti is dative = to the guest

So the structure tells you the role of the noun, even though the form alone could match more than one case.

Because acre is the correct neuter form of the adjective acer, acris, acre.

This adjective belongs to the third declension, not the first/second declension. Its forms are different from adjectives like bonus, bona, bonum.

For acer, acris, acre:

• masculine nominative singular: acer
• feminine nominative singular: acris
• neuter nominative singular: acre

Since vinum is neuter singular, the adjective must agree with it:

• vinum acre

not vinum acrum

So acre agrees correctly with vinum in gender, number, and case.

Placet means it pleases or is pleasing.

It is the third-person singular present active indicative of placeo, placere.

So:

• placet = it pleases / is pleasing
• non placet = it does not please / is not pleasing

In smoother English, we often translate this as does not like, but the Latin structure is really:

• Vinum acre hospiti non placet
  = The sharp/bitter wine is not pleasing to the guest

Understanding that literal structure helps a lot with dative nouns after placeo.

Because non normally negates the word or idea that follows, and very often it comes directly before the verb.

So:

• non placet = does not please

That is the most natural placement here. Latin word order is flexible, so you may sometimes see non elsewhere for emphasis, but non placet is straightforward and standard.

Because Latin has no articles.

There is no direct equivalent of English the, a, or an in ordinary Latin. So vinum acre can mean:

• the sharp wine
• a sharp wine
• simply sharp wine

Which one sounds best depends on the context and on the English translation you are aiming for.

That is completely normal in Latin.

Yes. Latin word order is much freer than English word order because the endings show the grammatical relationships.

So all of these could express basically the same idea:

• Vinum acre hospiti non placet
• Hospiti vinum acre non placet
• Non placet hospiti vinum acre

However, word order can affect emphasis. For example:

• putting hospiti earlier may highlight the guest
• putting non placet earlier may highlight the fact that it is not pleasing

The sentence you have is a normal and clear arrangement.

Potentially either, because hospes, hospitis can mean guest, host, or sometimes stranger, depending on context.

So hospiti is the dative singular and could mean:

• to the guest
• to the host

Usually the wider context makes the intended meaning clear. If your given translation says guest, then that is the sense to use here.

Acre comes from acer, acris, acre, which can mean things like:

• sharp
• pungent
• harsh
• bitter
• sour

With wine, the exact English word depends on context and on what nuance the translator wants. It could suggest wine that is:

• too sharp-tasting
• sour
• harsh

So even if the general meaning is clear, the adjective may carry slightly different shades in different contexts.

Because the subject is singular:

• vinum acre = the sharp wine

Since there is only one grammatical subject, the verb is singular:

• placet = is pleasing

If the subject were plural, the verb would also be plural:

• vina acria hospiti non placent
  = The sharp wines are not pleasing to the guest

So the verb agrees with vinum, not with hospiti.