Za mene je jedna mala porcija sasvim dovoljna.

Za mene literally means for me.

In this sentence, za mene expresses a personal point of view:
As far as I’m concerned / for me, one small portion is enough.

You could also hear Meni je jedna mala porcija sasvim dovoljna.
That version is also natural, and it means almost the same thing.

A useful difference:

• za mene = for me, from my perspective
• meni = to me, often used with expressions like it is enough to me / for me

So both are possible, but za mene sounds a bit more like the speaker is giving their personal standard or preference.

Croatian has a rule that short unstressed forms, called clitics, tend to come in the second position of the clause.

Here, je is the short form of biti (to be), meaning is.

So in:

Za mene je jedna mala porcija sasvim dovoljna.

the first unit is Za mene, and then the clitic je comes right after it.

This is very normal in Croatian word order. English speakers often expect the verb to stay directly after the subject, but Croatian is more flexible.

Jedna means one, and here it emphasizes the quantity: one small portion.

So the sentence is not just saying a small portion in a vague way, but specifically one small portion.

Croatian often uses jedan / jedna / jedno where English might simply use a/an or no article at all.

Compare:

• mala porcija = a small portion / small portion
• jedna mala porcija = one small portion

Including jedna can make the sentence feel a little more concrete or emphatic.

Because they all agree with porcija, which is a feminine singular noun.

Croatian adjectives and adjective-like words must agree with the noun in:

• gender
• number
• case

Here:

• porcija = feminine singular
• jedna = feminine singular form of one
• mala = feminine singular form of small
• dovoljna = feminine singular form of enough / sufficient

So all of them match porcija.

Porcija is in the nominative singular.

That is because it is the subject of the sentence:

jedna mala porcija = one small portion

The sentence structure is basically:

[For me] [is] [one small portion] [completely enough].

Even though Croatian word order is flexible, jedna mala porcija is still the thing being described as dovoljna.

Yes, English enough does not change form, but Croatian adjectives do.

Dovoljan / dovoljna / dovoljno means enough or sufficient, and its form changes to match the noun it describes.

Here it describes porcija, which is feminine singular, so the correct form is:

• dovoljan = masculine singular
• dovoljna = feminine singular
• dovoljno = neuter singular

Examples:

• Sendvič je dovoljan. = The sandwich is enough.
• Porcija je dovoljna. = The portion is enough.
• Jelo je dovoljno. = The dish/food is enough.

Sasvim means something like:

• completely
• quite
• perfectly

So sasvim dovoljna means:

• completely sufficient
• quite enough
• perfectly enough (less natural in English, but close in force)

It strengthens dovoljna.
The speaker is not saying the portion is barely enough, but that it is fully enough.

Yes.

Za mene je jedna mala porcija dovoljna.
This means For me, one small portion is enough.

Adding sasvim makes it stronger or more reassuring:

Za mene je jedna mala porcija sasvim dovoljna.
= For me, one small portion is quite / completely enough.

So sasvim is optional, but it adds emphasis.

Yes, and that would also sound natural:

Za mene je mala porcija sasvim dovoljna.

That means For me, a small portion is quite enough.

The version with jedna emphasizes the quantity one a bit more.
The version without it is a little more general.

That version is also grammatically possible. Croatian word order is flexible, and changing the order often changes the focus rather than the basic meaning.

Compare:

• Za mene je jedna mala porcija sasvim dovoljna.
  Focuses first on for me.

• Jedna mala porcija je za mene sasvim dovoljna.
  Starts with one small portion, so that gets more attention.

Croatian speakers often move elements around depending on what they want to emphasize.

Yes, porcija is a common word. It means:

• portion
• serving

It is often used for food in restaurants, at home, or when talking about quantity.

Examples:

• velika porcija = a large portion
• mala porcija = a small portion
• dvije porcije = two portions

So in this sentence, it clearly refers to an amount of food.

Yes, that is a good natural translation.

Depending on how closely you want to reflect the Croatian, you could also say:

• One small portion is enough for me.
• For me, one small portion is quite enough.
• As for me, one small portion is completely sufficient.

The most natural everyday English version is probably:

A small portion is enough for me
or
One small portion is enough for me

It is neutral and natural in both spoken and written Croatian.

Nothing in it is especially formal or slangy. You could say it:

• in a restaurant
• at home
• in conversation about food
• in writing

If anything, sasvim dovoljna sounds a little more careful or polite than a very short casual answer, but it is still completely everyday Croatian.