De slang is lang.

In this sentence, slang is the Dutch noun meaning snake.

So:

• de slang = the snake
• slang in English = informal speech

This is a false friend for English speakers. Dutch can also use slang in the English sense in some contexts, but in a basic sentence like De slang is lang, it clearly means the snake.

De is the Dutch definite article meaning the.

Dutch has two main words for the:

• de
• het

Every noun has to be learned with its article. Slang is a de-word, so you say:

• de slang = the snake

There is not always a logical reason you can predict from meaning alone, so learners usually memorize nouns together with their article.

Yes. Is is the third-person singular form of the Dutch verb zijn (to be).

So:

• ik ben = I am
• jij bent / ben jij = you are
• hij/zij/het is = he/she/it is

In De slang is lang, de slang is singular, so is is the correct form.

Yes, this sentence has the same basic order as English:

• De slang = subject
• is = verb
• lang = adjective/complement

So it is literally:

• The snake is long.

This is a simple Dutch main clause with normal word order: subject + verb + complement.

Because lang comes after the verb is here, so it is a predicative adjective. In Dutch, predicative adjectives usually do not take the -e ending.

Compare:

• De slang is lang. = The snake is long.
  → after the verb, so lang

But:

• de lange slang = the long snake
  → before the noun, so lange

This is an important Dutch pattern:

• de man is groot = the man is tall
• de grote man = the tall man

A rough English-friendly guide:

• slang sounds somewhat like slahng
• lang sounds like lahng

Important points:

• The a in lang is a long vowel in Dutch.
• The ng is like the sound at the end of English sing.
• slang and lang rhyme.

If you know IPA, a common pronunciation is roughly:

• slang /slɑŋ/
• lang /lɑŋ/

Depending on accent, the exact vowel quality may vary a bit.

This is a common spelling question in Dutch.

In a closed syllable (a syllable ending in a consonant), Dutch often writes a long vowel with one vowel letter if the following consonant pattern already signals the pronunciation.

So:

• lang = long vowel sound
• lange keeps the same base word when an ending is added

Dutch spelling rules can feel unfamiliar at first, but with common words like lang, it is best to learn the pronunciation together with the spelling.

Yes. Lang is the normal Dutch adjective for long.

Examples:

• een lange weg = a long road
• De film is lang. = The movie is long.
• lang haar = long hair

Be careful not to confuse:

• lang = long
• groot = big / large
• hoog = high / tall (for some things)
• groot can also mean tall for people in some contexts

For a snake, lang is exactly the natural word if you mean its length.

Yes. The plural of slang is slangen.

So:

• de slang = the snake
• de slangen = the snakes

The plural version of the sentence would be:

• De slangen zijn lang. = The snakes are long.

Notice that the verb changes:

• singular: is
• plural: zijn

It is grammatically correct and understandable Dutch, but it also feels a bit like a teaching sentence because of the rhyme-like pattern:

• slang
• lang

A native speaker could certainly say it, especially in a simple description, but in real conversation they might more often say something slightly fuller, such as:

• Die slang is erg lang. = That snake is very long.
• De slang is heel lang. = The snake is very long.

So yes, it is natural enough, but it is also especially useful as a beginner sentence because it is short and memorable.

No. In Dutch, you capitalize the first word of the sentence:

• De slang is lang.

But nouns are not capitalized in Dutch the way they are in German.

So:

• de slang = correct
• de Slang = not correct, unless it is part of a name or title

Yes, but it changes the meaning.

• De slang is lang. = The snake is long.
  This refers to a specific snake.

• Een slang is lang. = A snake is long.
  This sounds more general, but it is a bit odd as a general statement because not every snake is equally long.

If you are talking about one particular snake you can see or have already mentioned, de slang is the better choice.