Nemam nikakav plan, ali bih rado otišla u kratku šetnju.

Croatian often drops subject pronouns when the verb already makes the subject clear.

• nemam = I do not have
• bih = I would

So ja is unnecessary unless you want emphasis or contrast:

• Nemam nikakav plan... = neutral
• Ja nemam nikakav plan... = I don’t have any plan (maybe someone else does)

Nikakav means something like:

• no
• not any
• literally of no kind

So:

• Nemam nikakav plan = I don’t have any plan at all / I have no plan whatsoever

It is stronger than just nemam plan. It adds emphasis that there is really no plan.

Because Croatian normally uses negative concord. That means if the verb is negative, other negative-type words usually stay negative too.

So Croatian says:

• Nemam nikakav plan.

Literally, that may look like I don’t have no kind of plan to an English speaker, but in Croatian that is the normal grammar, not a double negative mistake.

Because plan is the direct object of imati (to have), so it is in the accusative.

For a masculine inanimate singular noun like plan, the accusative looks the same as the nominative:

• nominative: plan
• accusative: plan

So the form does not change.

You may sometimes see genitive after negation in older or more literary language, but in modern standard Croatian, nemam plan is normal.

Bih is the 1st person singular conditional auxiliary. It is used to form would-type meanings.

Here:

• bih otišla = I would go

The Croatian conditional is usually formed with:

• bih, bi, bismo, biste, bi
• the l-participle of the main verb

Examples:

• ja bih otišla = I would go
• ti bi otišao = you would go
• mi bismo otišli = we would go

Because otišla is the feminine singular form, so the speaker is understood to be female.

Compare:

• otišao = masculine singular
• otišla = feminine singular

So:

• ali bih rado otišla... = said by a woman
• ali bih rado otišao... = said by a man

Rado means:

• gladly
• with pleasure
• willingly

So:

• bih rado otišla = I would gladly go / I’d be happy to go

It is a very common Croatian word for expressing willingness in a natural way.

Examples:

• Rado pomažem. = I gladly help.
• Rado bih došla. = I would gladly come.

U kratku šetnju is in the accusative, because it expresses motion toward something.

• šetnja is a feminine noun
• accusative singular: šetnju
• adjective must agree: kratku

So:

• u kratku šetnju = for a short walk

This is similar to the general pattern:

• u
  • accusative = movement into/toward
• u
  • locative = location in/inside

Compare:

• Idem u grad. = I’m going to the city.
• U gradu sam. = I’m in the city.

Because Croatian uses a different idiomatic structure.

The phrase ići / otići u šetnju is a normal Croatian way to say:

• to go for a walk

So even though u often means into or to, here the whole phrase is best understood as a set expression.

You should learn u šetnju as a natural collocation with verbs like:

• ići u šetnju
• otići u šetnju

Yes, Croatian word order is somewhat flexible, but bih is a clitic, so it tends to appear in an early position in the clause.

The given version:

• ali bih rado otišla...

is natural and standard.

You may also hear variations like:

• ali rado bih otišla...

The difference is mostly one of style, rhythm, or emphasis, not basic meaning.

For learners, the safest thing is to remember that forms like bih usually do not stand freely anywhere you want.

This is about aspect.

• ići = imperfective
• otići = perfective

In this sentence, otišla suggests a more complete, single action: go off / head out for a walk.

So:

• bih rado otišla u kratku šetnju = I’d gladly go out for a short walk

If you used išla, it would sound a bit different and less natural here in many contexts. With a one-time idea or suggestion like this, otići works very well.

Croatian can use the singular here very naturally:

• Nemam nikakav plan = I don’t have any plan / I have no particular plan

This often means there is no specific idea or arrangement.

If you want a more literal I don’t have any plans, Croatian can also say:

• Nemam nikakvih planova.

So both singular and plural are possible, but the singular in your sentence sounds very natural.

Because ali means but and joins two separate clauses:

• Nemam nikakav plan
• ali bih rado otišla u kratku šetnju

In standard Croatian writing, a comma is normally used before ali in this kind of sentence.

So the punctuation here is correct and expected.