Zbog kiše moramo promijeniti plan za vikend.

Because zbog requires the genitive case in Croatian. The noun kiša changes to its genitive singular form kiše.

• nominative: kiša = rain
• genitive: kiše = of rain / because of rain after zbog

So zbog kiše means because of the rain / because of rain.

Zbog means because of, due to, or on account of. It is used to give a reason or cause.

In this sentence, zbog kiše gives the reason why the plan has to change.

Moramo means we must or we have to. It is the 1st person plural form of morati.

• moram = I must
• moraš = you must
• mora = he/she/it must
• moramo = we must

So moramo promijeniti means we have to change.

This is about aspect, which is very important in Croatian.

• promijeniti = perfective, meaning to change something completely, as a finished action
• mijenjati = imperfective, meaning to be changing, to change repeatedly, or focusing on the process

Here, the sentence refers to one complete change of plan, so promijeniti is the natural choice.

Croatian does not use articles like a, an, or the. That idea is usually understood from context.

So:

• plan can mean a plan or the plan
• vikend can mean a weekend or the weekend

In this sentence, English naturally says the plan for the weekend, but Croatian simply says plan za vikend.

Za vikend means for the weekend or often on/during the weekend, depending on context.

Here it modifies plan:

• plan za vikend = plan for the weekend

The preposition za often takes the accusative case, and vikend here is in the accusative singular. Since vikend is an inanimate masculine noun, its accusative form is the same as the nominative, so it still looks like vikend.

Yes, Croatian word order is more flexible than English word order, because case endings show grammatical relationships.

The neutral order here is:

Zbog kiše moramo promijeniti plan za vikend.

But other orders are possible, for example:

• Moramo zbog kiše promijeniti plan za vikend.
• Plan za vikend moramo promijeniti zbog kiše.

These versions are all grammatical, but they may shift emphasis slightly. The original sentence sounds very natural and neutral.

Because the sentence is talking about one plan for the weekend, not several plans.

• plan = plan
• planovi = plans

So promijeniti plan means to change the plan or to change our plan.

It is singular.

• nominative singular: kiša
• genitive singular: kiše
• nominative plural: kiše

So kiše can sometimes look ambiguous, but after zbog, it is understood as genitive singular here: because of rain.

A rough pronunciation guide is:

Zbog kiše moramo promijeniti plan za vikend
≈ zbog KEE-sheh mo-RA-mo pro-MYAY-nee-tee plahn zah VEE-kend

A few helpful points:

• ž sounds like the s in measure
• š sounds like sh
• j sounds like English y
• c sounds like ts
• r is rolled or tapped more than in English

Yes, radi kiše is possible and also means because of the rain / due to the rain, and radi also takes the genitive.

However, zbog kiše is usually the more common and straightforward choice in everyday speech. For a learner, zbog is the safest and most useful option to remember first.