Learn Hardcore Czech: Oslava, kterou plánujeme v muzeu, bude krátká, ale plná hudby a umění. - The celebration that we are planning in the museum will be short but full of music and art.

In the relative clause kterou plánujeme v muzeu, the celebration is the object of the verb plánujeme (we are planning [it]), not the subject.
So we need the accusative form: kterou.

If the celebration were the subject of that clause, we would use která, for example:

Oslava, která bude v muzeu, bude krátká.
The celebration that will be in the museum will be short.

What is the role of the commas around kterou plánujeme v muzeu?

The part kterou plánujeme v muzeu is a relative clause giving extra information about Oslava. In Czech, such “non‑essential” relative clauses are set off by commas on both sides:

Oslava, kterou plánujeme v muzeu, bude krátká…

The commas show that:

the main clause is Oslava bude krátká, ale plná hudby a umění.
the middle part kterou plánujeme v muzeu is an inserted description (which we are planning in the museum), not a separate main clause.

Why is it v muzeu and not v muzeum?

The preposition v meaning “in/at” with a static location (no movement) requires the locative case.

muzeum is the dictionary form (nominative singular).
Its locative singular is muzeu.

So:

v muzeu = in the museum (locative)
There is no correct form v muzeum in standard Czech for location.

If you wanted to say “into the museum” (movement), you would normally use do + genitive:

do muzea = into the museum

Why is it bude krátká and not bude krátké or bude krátký?

The adjective must agree with oslava in gender, number, and case:

oslava = feminine, singular, nominative
So the adjective in the predicate position is krátká (fem. sg. nom.)

Forms:

krátký = masculine
krátké = neuter (or some plural forms)
krátká = feminine → matches oslava

The future tense is bude (3rd sg.) + adjective:

(Ta) oslava bude krátká.
The celebration will be short.

Why do we repeat a separate adjective plná instead of saying something like bude krátká, ale hudby a umění plná?

In Czech, it’s most natural to repeat the predicate adjective when you want to contrast two qualities:

bude krátká, ale plná hudby a umění
will be short but full of music and art

Both krátká and plná agree with oslava (feminine singular nominative).
You can say bude krátká, ale hudby a umění plná and it is grammatical, but it sounds more literary/marked. The original word order (krátká, ale plná…) is the neutral, everyday choice.

Why is plná followed by hudby a umění in the genitive, not by nominative forms like hudba a umění?

The adjective plný / plná typically takes the genitive case to mean “full of something”:

plná hudby = full of music (hudby = genitive of hudba)
plná umění = full of art (umění = genitive of umění, same form as nominative)

So plná hudby a umění literally means “full of music and (of) art”.

Using nominative here (plná hudba a umění) would change the structure and be incorrect in this meaning.

Could we say plná hudbou a uměním instead? What would that mean?

plná hudbou a uměním uses the instrumental case (hudbou, uměním).

plná + genitive (hudby, umění) = the standard idiom for “full of music and art” (content)
plná + instrumental can sound more like “filled/covered with music and art” as instruments/means or surrounding circumstances; it’s possible in poetic or specific contexts, but it’s not the neutral way to express “full of X” in general.

In everyday language, for “full of music and art” you almost always choose:

plná hudby a umění (genitive), as in the sentence.

Why is there a comma before ale?

In Czech, when ale connects two clauses (each with its own verb or full predicate), you put a comma before it:

Oslava … bude krátká, ale plná hudby a umění.

Here the predicate is complex (“bude krátká” and “(bude) plná hudby a umění”), but it’s treated like two coordinated parts of the sentence, so a comma is standard before ale.

If ale connects just two words or short phrases without separate predicates, you may or may not use a comma depending on structure, but with clause‑level contrast like this, the comma is expected.

Can we move v muzeu earlier and say Oslava, v muzeu kterou plánujeme, bude krátká…?

Grammatically it’s possible, but it sounds unnatural and somewhat clumsy.

The most natural order is:

kterou plánujeme v muzeu
The adverbial phrase v muzeu follows the verb it modifies (plánujeme).

You could also say:

kterou v muzeu plánujeme

This is still acceptable and might add a little emphasis to v muzeu, but the original version is smoother and more neutral in everyday speech.

Why is it plánujeme and not naplánujeme in this sentence?

plánujeme is the imperfective verb plánovat (we are planning / we plan).
naplánujeme is perfective (we will plan / we will have planned).

In the relative clause:

kterou plánujeme v muzeu
suggests an ongoing or general action: the celebration that we are (in the process of) planning in the museum.

If you used kterou naplánujeme v muzeu, it would point more to a completed act in the future:

the celebration that we will (successfully) plan in the museum

In the context of describing an event being arranged, plánujeme (imperfective) is the natural choice.

Why don’t we say my plánujeme? How do we know who is planning?

In Czech, the personal pronoun is usually dropped because the verb ending already shows the person and number:

plánujeme = first person plural (we plan / we are planning)

Adding my is only needed for emphasis or contrast:

My plánujeme oslavu v muzeu, ne oni.
We are planning the celebration in the museum, not them.

In the sentence Oslava, kterou plánujeme v muzeu…, it’s clear from -eme that the subject is “we”, so my is omitted.

Is there any difference in meaning between Oslava, kterou plánujeme v muzeu, bude krátká… and Oslava, kterou plánujeme, bude v muzeu krátká…?

Yes, the placement of v muzeu changes which part it modifies:

Oslava, kterou plánujeme v muzeu, bude krátká…
- v muzeu modifies plánujeme → we are planning it in the museum
  The planning takes place in/at the museum.
Oslava, kterou plánujeme, bude v muzeu krátká…
- v muzeu now most naturally modifies bude krátká → it will be short in the museum
  It sounds like the celebration will be short when/where it takes place in the museum, not necessarily that the planning happens there.

So word order in Czech is quite flexible, but it can subtly change which element a phrase like v muzeu is understood to belong to.