Learn Hardcore German: Die Redewendung „ins kalte Wasser springen“ finde ich lustig und sehr bildlich. - I find the idiom “to jump into cold water” funny and very vivid.

In Die Redewendung „ins kalte Wasser springen“ finde ich …, why does the verb finde come before ich? I thought the subject goes before the verb.

German main clauses follow the verb‑second (V2) rule:

The finite verb (here: finde) must be in second position.
The first position can be taken by any element (subject, object, adverbial, etc.).

In your sentence, the first position is taken by the long object:

1st position: Die Redewendung „ins kalte Wasser springen“
2nd position: finde (finite verb)
Rest: ich lustig und sehr bildlich.

So the order is: [object] – [verb] – [subject] – [rest].

If you put the subject first, you get the more neutral:

Ich finde die Redewendung „ins kalte Wasser springen“ lustig und sehr bildlich.

Both are correct; the original version simply emphasizes the expression itself by putting it first.

Is Die Redewendung „ins kalte Wasser springen“ the subject or the object of finden?

It is the direct object of finden.

Logically, the structure is:

ich = subject (the one who finds something funny)
finde = verb
die Redewendung „ins kalte Wasser springen“ = accusative object
lustig und sehr bildlich = object complement (what I think about the idiom)

German allows the object to move to the first position for emphasis, which is why it appears before the verb.

You can see the same roles more clearly in the “normal” order:

Ich (subject) finde die Redewendung „ins kalte Wasser springen“ (object) lustig und sehr bildlich.

What case is ins kalte Wasser and what exactly is ins?

ins is the contraction of in das:

in (preposition)
das (neuter accusative singular article)
→ in + das = ins

The phrase ins kalte Wasser is in the accusative case.

Reason: in can take either dative (location: in der Schule = in the school) or accusative (direction/motion: in die Schule = into the school).

The verb springen involves movement into something, so German uses accusative:

in das kalte Wasser springen → ins kalte Wasser springen
= to jump into the cold water

Why is the adjective ending kalte and not kaltes or something else?

Fully written out, the phrase is:

in das kalte Wasser (before contraction)

The noun Wasser is:

gender: neuter
case: accusative
number: singular
article: das (definite article)

With a definite article, adjectives take the weak declension. For neuter accusative singular with das, the adjective ending is -e:

das kalte Wasser

So:

not das kaltes Wasser (wrong ending)
but das kalte Wasser

After contraction you get:

ins kalte Wasser = in das kalte Wasser

The -e ending on kalte is exactly what the weak declension requires here.

Why is the idiom shown in the infinitive ins kalte Wasser springen instead of a conjugated form?

Idioms and verbs in German are usually cited in the infinitive when you talk about them as expressions:

das Verb gehen
die Redewendung ins kalte Wasser springen
die Phrase etwas auf die leichte Schulter nehmen

You are not using the idiom here; you are naming it. When you name an expression, you normally give its dictionary form (infinitive for verbs).

If you used it in a sentence, you would conjugate it:

Ich bin gestern ins kalte Wasser gesprungen.
Manchmal muss man einfach ins kalte Wasser springen.

Can I also say Ich finde die Redewendung „ins kalte Wasser springen“ lustig und sehr bildlich? Is there any difference?

Yes, that sentence is completely correct.

The difference is mainly in emphasis and style:

Die Redewendung „ins kalte Wasser springen“ finde ich lustig und sehr bildlich.
- Puts die Redewendung … at the beginning → emphasizes the expression itself.
- Slightly more stylistic / written feeling.
Ich finde die Redewendung „ins kalte Wasser springen“ lustig und sehr bildlich.
- More neutral and very common in spoken German.
- Emphasis is more on ich finde … (your opinion).

Grammatically, both are fine; it’s just a matter of what you want to highlight.

What is the nuance of lustig here? Does it mean “funny”, “fun”, or “silly”?

lustig can cover several meanings, depending on context:

amusing / funny
- Der Film war lustig. – The film was funny / made me laugh.
cheerful / in a good mood
- Sie ist heute ganz lustig. – She’s in a cheerful mood today.
In some contexts, a bit strange / odd (colloquial, often with a tone of criticism):
- Das ist aber lustig … – That’s a bit strange …

In Die Redewendung „ins kalte Wasser springen“ finde ich lustig, it means:

I find the idiom amusing / funny (it makes me smile).

It does not mean “silly” or “stupid” here; it’s a positive, light description.

What does bildlich mean here? How is it different from anschaulich or metaphorisch?

bildlich literally relates to Bilder (pictures). In this context it means:

figurative / image-rich / easy to picture in your mind

So:

bildliche Sprache – figurative language, language that creates images.
sehr bildlich – very pictorial, very vivid in imagery.

Comparison:

bildlich: focuses on the mental picture you get; good word for talking about idioms.
anschaulich: “vivid, clear, easy to understand” (e.g. a good explanation, a clear example).
- ein anschauliches Beispiel – a vivid / clear example.
metaphorisch: explicitly “metaphorical” (technical/linguistic term).
- Das ist nur metaphorisch gemeint.

In your sentence, sehr bildlich says that the idiom creates a strong mental image, which is exactly what idioms often do.

Why is there no comma before und sehr bildlich?

Here, lustig and sehr bildlich are just two predicate adjectives joined by und:

… finde ich lustig und sehr bildlich.

In German, when you connect two equal parts (adjectives, nouns, verbs) with und or oder, you normally don’t use a comma:

Er ist groß und stark.
Sie ist klug und fleißig.
Ich esse gern Pizza und Pasta.

A comma would only appear if und connects larger units such as whole clauses:

Ich finde die Redewendung lustig, und ich benutze sie oft.
(two main clauses → comma)

Why is it die Redewendung and not der Redewendung or das Redewendung? How can I know the gender?

Redewendung is feminine, so the correct article is die:

die Redewendung – the idiom / expression

A good rule of thumb: almost all nouns ending in ‑ung are feminine:

die Zeitung (newspaper)
die Rechnung (bill)
die Meinung (opinion)
die Bedeutung (meaning)
die Redewendung (idiom)

So:

Nom./Acc. singular: die Redewendung
Dat. singular: der Redewendung
Gen. singular: der Redewendung

Some related words with different genders:

die Wendung (feminine) – turn/phrase
der Ausdruck (masculine) – expression
die Phrase (feminine) – phrase (often negative: empty phrase)

But as soon as you see ‑ung, the safe guess is die.

Why are the quotation marks written as „…“ in German and not like English "..."?

German typographical quotation marks are usually:

opening: „ (bottom left)
closing: “ (top right)

So your sentence uses standard German-style quotes:

Die Redewendung „ins kalte Wasser springen“ finde ich …

In many digital contexts (especially informal ones), Germans also just use the straight English-style marks "...", but in printed texts, books, and careful writing you’ll often see „…“.

Both are understood; the „…“ variant is simply the typographical standard in German.