Ako želite, mogu vam poslati fotografiju portreta koji mi se najviše svidio.

Želite is the 2nd person plural form of željeti (to want).

In Croatian, that form is used in two ways:

• when speaking to more than one person
• when speaking politely to one person (like you in formal English)

So Ako želite means:

• If you want (formal singular), or
• If you want (plural)

By contrast, želiš is singular informal, used with one person you address as ti.

Because Ako želite is a dependent clause meaning if you want.

Croatian normally separates this kind of introductory clause from the main clause with a comma:

• Ako želite, mogu vam poslati...

This is very natural and standard.
The main clause begins with mogu vam poslati.

Because mogu is a modal verb meaning I can.

After modal verbs in Croatian, the next verb usually stays in the infinitive:

• mogu poslati = I can send
• želim doći = I want to come
• moram ići = I must go

So:

• mogu = I can
• poslati = to send

Together: I can send

Croatian often leaves out subject pronouns when they are already clear from the verb ending.

• mogu already means I can
• so ja is not necessary

You could say ja mogu, but that adds emphasis, like:

• I can send it / I am able to send it

Without ja, the sentence sounds neutral and natural.

Vam means to you.

It is the dative form of vi.
Here it marks the indirect object: the person who would receive the photo.

So:

• mogu vam poslati fotografiju = I can send you a photo
• literally: I can send a photo to you

Compare:

• ti = informal singular you
• vam = formal singular or plural to you

Because fotografiju is in the accusative singular.

It is the direct object of poslati (to send):
the thing being sent is the photo.

Basic pattern:

• nominative: fotografija = photo
• accusative: fotografiju = photo as a direct object

So:

• Fotografija je lijepa. = The photo is beautiful.
• Šaljem fotografiju. = I am sending the photo / a photo.

This means a photo of the portrait.

Portreta is the genitive singular of portret.
After nouns like fotografija (photo), Croatian often uses the genitive to show what the photo is of.

So:

• fotografija portreta = a photo of the portrait
• literally: photo of portrait

This is a very common Croatian structure:

• fotografija grada = a photo of the city
• slika mora = a picture of the sea

Koji refers to portreta — in dictionary form, portret.

Even though the word appears as portreta in the sentence, the noun itself is still:

• portret = masculine singular

The relative pronoun koji must agree with the noun it refers to in gender and number, so it is masculine singular.

The clause means:

• portreta koji mi se najviše svidio
• the portrait that I liked the most

Because inside the relative clause, the pronoun is the subject of svidio se.

In the relative clause:

• koji mi se najviše svidio
• literally: which pleased me the most

Since it is the subject there, it must be in the nominative singular:

• koji

Important point:
the case of koji depends on its role in the relative clause, not on the form of portreta before it.

So even though portreta is genitive because of fotografiju portreta, the relative pronoun is nominative because it functions as the subject of svidio se.

Croatian often expresses to like with the verb svidjeti se, which works differently from English.

Instead of:

• I liked the portrait

Croatian structures it more like:

• The portrait pleased me

So in:

• koji mi se najviše svidio

the parts are:

• mi = to me / me in dative
• se = a fixed part of svidjeti se
• svidio = past tense masculine singular form

Literally, this is close to:

• which appealed to me the most
• which pleased me the most

That is why mi is in the dative, not nominative.

Because svidjeti se takes the person who experiences the liking in the dative, not the accusative.

So:

• mi se sviđa = I like it / literally it is pleasing to me
• ti se sviđa = you like it
• mu se sviđa = he likes it
• joj se sviđa = she likes it

Here:

• mi se najviše svidio = I liked ... the most

So mi is correct because the verb requires dative.

Because the verb form agrees with portret, which is masculine singular.

In the past tense, Croatian participles agree in gender and number with the subject:

• portret se svidio = masculine singular
• slika se svidjela = feminine singular
• pismo se svidjelo = neuter singular

Here the subject is the relative pronoun koji, referring back to portret, so we get:

• koji mi se najviše svidio

not svidjela, because the noun is not feminine.

Najviše means the most.

It is the superlative form of mnogo / više / najviše in this kind of usage.

So:

• svidio mi se = I liked it
• više mi se svidio = I liked it more
• najviše mi se svidio = I liked it the most

In this sentence, it tells you that out of several portraits, this was the one the speaker liked most.

Because poslati is perfective, while slati is imperfective.

Croatian often uses the perfective infinitive after mogu when talking about one complete action:

• mogu vam poslati fotografiju = I can send you a photo
  (a single completed sending)

By contrast, slati would suggest repeated, ongoing, or more process-oriented sending.

So here poslati is the natural choice.

The sentence can be rearranged somewhat, but the original order is very natural.

Original:

• Ako želite, mogu vam poslati fotografiju portreta koji mi se najviše svidio.

Croatian word order is flexible, but not random.
Short unstressed words like vam, mi, and se tend to go in early positions in the clause.

For example, these are possible with different emphasis:

• Ako želite, mogu vam poslati fotografiju portreta...
• Fotografiju portreta koji mi se najviše svidio mogu vam poslati, ako želite.

But the original sounds the most neutral and natural for everyday use.

In this sentence, it naturally refers to portret, not fotografiju.

Why?

Because the form svidio is masculine singular, which matches:

• portret = masculine

But fotografija is feminine, so if the clause referred to fotografiju, you would expect:

• fotografiju ... koja mi se najviše svidjela

Since the sentence has koji ... svidio, the reference is clearly to portret.

So the meaning is:

• a photo of the portrait that I liked the most

not:

• the photo that I liked the most