Learn Hardcore Czech: Nechtěl bych ztratit svoji peněženku v parku. - I would not like to lose my wallet in the park.

Nechtěl bych is a conditional form and corresponds to “I wouldn’t like / I wouldn’t want.”
Nechci is present tense and means “I don’t want.”

So:

Nechci ztratit svoji peněženku v parku. = a direct, factual statement about your current will: I don’t want to lose my wallet in the park.
Nechtěl bych ztratit svoji peněženku v parku. = softer, more hypothetical or polite: I wouldn’t like to lose my wallet in the park (it would be bad if that happened).

Czech often uses this conditional to sound less blunt, especially when talking about undesirable possibilities or being polite.

How is the conditional Nechtěl bych formed?

The conditional in Czech is formed from:

the past tense form of the verb
plus a conditional auxiliary (bych, bys, by, bychom, byste, by)

For chtít (to want):

past masculine singular: chtěl
negative: nechtěl

Add the 1st person singular conditional auxiliary bych:

chtěl bych = I would want
nechtěl bych = I would not want / I wouldn’t like

Other persons:

(já) nechtěl bych – I would not want
(ty) nechtěl bys – you would not want
(on) nechtěl by – he would not want
(my) nechtěli bychom – we would not want
(vy) nechtěli byste – you (pl/pol) would not want
(oni) nechtěli by – they would not want

Where can bych go in the sentence? Can I move it?

Bych is a clitic and usually wants to be in the second position in the clause.

Your sentence is normal:

Nechtěl bych ztratit svoji peněženku v parku.

If you add já, the pronoun, you still keep bych early:

Já bych nechtěl ztratit svoji peněženku v parku.

Other natural variants:

Nechtěl bych svoji peněženku ztratit v parku.
V parku bych nechtěl ztratit svoji peněženku.

But you cannot put bych at the very end, like:

✗ Nechtěl ztratit svoji peněženku v parku bych. (wrong / very unnatural)

Why is it svoji and not moji? What is special about svůj?

Czech has a reflexive possessive adjective svůj (with forms svůj / svoje / svou / svoji etc.).
You normally use svůj when:

the possessor is the subject of the sentence.

Here, the subject is (já) – I – and the wallet belongs to that same I, so Czech prefers:

Nechtěl bych ztratit svoji peněženku v parku.

instead of:

Nechtěl bych ztratit moji peněženku v parku.

The second is understandable and sometimes said, but in standard Czech, svůj is considered the correct and more natural choice whenever the subject owns the thing.

So is moji peněženku actually wrong here?

It is not completely wrong in everyday speech, but it is less standard.

Normative grammar says:

If the owner = the subject → use forms of svůj.
If the owner ≠ the subject → use můj (můj, moje, moji, mou…), or other possessives like tvůj, jeho, její.

So in careful or written Czech, the best choice here is:

Nechtěl bych ztratit svoji (svou) peněženku v parku.

You might still hear moji peněženku in conversation, but learners are strongly advised to master the svůj rule.

What grammatical form is peněženku, and why not peněženka?

Peněženka is a feminine noun meaning wallet.
In the sentence it is the direct object of ztratit (to lose), so it must be in the accusative singular.

Declension (simplified):

nominative (who? what?): peněženka – the wallet (subject)
accusative (who? what? as an object): peněženku – the wallet (object)

English keeps wallet the same in both roles, but Czech changes the ending:

Moje peněženka je nová. – My wallet is new. (subject → nominative)
Nechtěl bych ztratit svoji peněženku. – I wouldn’t like to lose my wallet. (object → accusative)

Why does svoji end with -i? How does it agree with peněženku?

Svoji is a form of the possessive adjective svůj and it must agree with the noun it describes in:

gender
number
case

Peněženku is:

feminine
singular
accusative

So svůj takes its feminine singular accusative form:

svou or svoji

Both are correct:

Nechtěl bych ztratit svou peněženku v parku.
Nechtěl bych ztratit svoji peněženku v parku.

You will hear svoji very often in spoken Czech; svou sometimes sounds a bit more formal or literary, but both are standard.

What case is v parku, and why is it parku?

The preposition v (in) usually takes the locative case when it expresses a static location (being somewhere, not moving into).

Park is a masculine inanimate noun:

nominative singular: park – park (as subject)
locative singular: parku – in the park, about the park

So:

Ten park je velký. – The park is big. (nominative)
Jsem v parku. – I am in the park. (locative)

Your sentence uses v parku because it describes where the losing would (hypothetically) happen – in the park, not motion into it.

Why is the verb ztratit used, and not ztrácet?

Czech distinguishes aspect:

ztratit – perfective: one completed act of losing, the result is important (the wallet is gone).
ztrácet – imperfective: ongoing, repeated, or habitual losing, or the process itself.

In this sentence you are talking about a single event that (you fear) might happen:

Nechtěl bych ztratit svoji peněženku v parku.
→ I wouldn’t like it if this one losing event happened.

If you said:

Nechtěl bych ztrácet svoji peněženku.

it would sound more like I wouldn’t like to keep losing my wallet (again and again) – a repeated or ongoing problem.

Can I leave out svoji and just say Nechtěl bych ztratit peněženku v parku?

Yes, you can.

Nechtěl bych ztratit peněženku v parku.

is perfectly grammatical and natural.
Often it is clear from context that the wallet is yours.

Adding svoji:

makes it explicit that it is your wallet
can add a bit of emphasis or clarity, especially in contexts where several people or wallets are involved

If there is no ambiguity, Czech speakers often omit possessives like this.

Is the word order fixed, or can I move parts of the sentence around?

Czech word order is relatively flexible, and you can move elements to emphasize them, as long as grammar (cases, agreement) stays right and bych remains early.

All of these are possible, with slightly different emphasis:

Nechtěl bych ztratit svoji peněženku v parku. (neutral)
V parku bych nechtěl ztratit svoji peněženku. (emphasis on in the park)
Svoji peněženku bych nechtěl ztratit v parku. (emphasis on my wallet rather than something else)
Já bych nechtěl ztratit svoji peněženku v parku. (I wouldn’t like to lose it, maybe someone else doesn’t mind)

What you cannot change is the internal grammar: peněženku must stay accusative, v parku must be locative, svoji must agree, etc.

How do you pronounce Nechtěl bych ztratit svoji peněženku v parku?

Approximate pronunciation, syllable by syllable (stress is always on the first syllable of each word):

Nechtěl – NECH-tyel
- ch like German Bach
- těl sounds a bit like tyel (soft t
  - ye)
bych – bikh (short i, final ch as in Bach)
ztratit – STRA-tit (cluster ztr- is pronounced together; both t are simple t)
svoji – SVO-yi (the j is like English y in yes)
peněženku – PE-nye-zhen-ku
- ně ~ nye
- ž like s in measure
- ku like koo
v – like English v (often very short, almost attached to the next word)
parku – PAR-ku (rolled or tapped r; ku like koo)

Rough IPA (for reference):
[ˈnɛxtjɛl bɪx ˈstr̩tat ˈsvojɪ pɛˈɲɛʒɛŋku f ˈparku] (details vary slightly by speaker).