Ako dođu gosti, dobro će nam doći još jedna stolica.

In Croatian, after ako (if), you normally do not use the future tense with će. Instead, Croatian usually uses the present tense of a perfective verb to refer to a future event.

So:

• Ako dođu gosti = If guests come
• not normally Ako će doći gosti

Here doći is a perfective verb (to come / to arrive as a completed event), and its present-tense form dođu often refers to the future in if-clauses.

This is very common in Croatian:

• Ako stigneš, nazovi me. = If you arrive / make it, call me.
• Ako padne kiša, ostat ćemo kod kuće. = If it rains, we’ll stay home.

Dođu is the 3rd person plural present tense of the verb doći (to come / arrive).

The subject is gosti (guests), which is plural, so the verb must also be plural:

• gost = guest
• gosti = guests
• dođu = they come / they arrive

So Ako dođu gosti literally means If guests arrive.

Yes, it can also come before the verb.

Croatian word order is more flexible than English word order. In this sentence:

• Ako dođu gosti...

the verb comes first and the subject follows it. This is completely natural.

You could also say:

• Ako gosti dođu...

That also means If the guests/guests come. The difference is mostly one of rhythm, focus, or style, not basic meaning.

Yes, this is a very common expression. Dobro doći means something like:

• to come in handy
• to be useful
• to be welcome
• to serve well

So:

• dobro će nam doći još jedna stolica

means:

• one more chair will come in handy for us
• we’ll be glad to have another chair
• another chair would be useful

Literally, it looks like will come well to us, but in natural English you would translate it idiomatically, not word for word.

Nam is the dative plural / 1st person plural clitic meaning to us.

In the expression dobro doći, the person who benefits is put in the dative:

• Trebat će mi pomoć. = I will need help.
• Dobro će ti doći odmor. = A rest will do you good / will come in handy for you.
• Dobro će nam doći još jedna stolica. = Another chair will come in handy for us.

So nam shows who the extra chair will be useful for.

Croatian has a group of short unstressed words called clitics, and će is one of them. Clitics usually appear in the second position of a clause.

In this clause:

• dobro će nam doći još jedna stolica

the clitic će comes very early, after the first stressed element dobro.

Also, nam is another clitic, so the sentence contains a little clitic cluster:

• će nam

This kind of placement is normal Croatian syntax, even if it feels unusual from an English perspective.

It can mean either one more chair or another chair, depending on context.

• još = still / yet / more
• jedna = one
• stolica = chair

Together, još jedna stolica means one additional chair.

So in English, the most natural translations are:

• one more chair
• another chair

Because stolica is a feminine noun, and the number one must agree with the noun in gender.

So:

• jedan = masculine
• jedna = feminine
• jedno = neuter

Examples:

• jedan gost = one guest
• jedna stolica = one chair
• jedno pitanje = one question

Since stolica is feminine, the correct form is jedna.

It can mean either, depending on context.

Croatian does not have articles like a or the, so gosti by itself can mean:

• guests
• the guests

In this sentence, English would probably most naturally say:

• If guests come... or
• If the guests come...

The wider context tells you which is intended.

Yes. That would also be correct, but the nuance is slightly different.

• Trebat će nam još jedna stolica. = We will need another chair.
• Dobro će nam doći još jedna stolica. = Another chair will come in handy / would be useful.

The version with trebati sounds a bit more direct and practical: the chair is needed.

The version with dobro doći sounds a little softer and more idiomatic: the chair would be useful or welcome.

Because Ako dođu gosti is a subordinate if-clause, and it is followed by the main clause:

• Ako dođu gosti, = If guests come,
• dobro će nam doći još jedna stolica. = another chair will come in handy for us.

Croatian normally uses a comma to separate this kind of subordinate clause from the main clause, just as English does in sentences like If guests come, we’ll need another chair.