Learn Hardcore German: Der Plan für den Urlaub ist speziell.

In German, the preposition für always takes the accusative case. Since Urlaub is a masculine noun (der Urlaub in the nominative), its accusative form is den Urlaub.

Why does speziell have no ending like spezielle or speziellen?

Here speziell is used predicatively (it follows the linking verb ist). Predicative adjectives in German remain uninflected, so you simply say Der Plan ist speziell. Only attributive adjectives (those placed directly before a noun) receive endings.

How would I say “a special plan for the vacation” with an indefinite article?

You need an attributive adjective with the correct ending: ein spezieller Plan für den Urlaub. Breakdown:

ein (nominative masculine indefinite article)
spezial
- -er (strong ending for nominative masculine)
Plan
für den Urlaub remains the same

Does speziell here mean “specific” or “special”?

In everyday usage, speziell means “special” or “unusual.” If you want the sense “specific,” you usually use spezifisch.

ein spezieller Plan = a special/unusual plan
ein spezifischer Plan = a specific plan

Can I say Der Plan ist speziell für den Urlaub instead of Der Plan für den Urlaub ist speziell?

Yes, both are grammatical.

Der Plan für den Urlaub ist speziell. (The vacation plan is special.)
Der Plan ist speziell für den Urlaub. (The plan is specifically intended for the vacation.)
The difference lies in emphasis and interpretation of speziell.

Why do we use the article den with Urlaub? Isn’t Urlaub an uncountable noun?

While Urlaub can refer to the general concept of taking time off, here you refer to a specific vacation. In German, when you speak of a definite instance of a usually uncountable noun, you use the article: den Urlaub = that particular vacation.

Why is Urlaub a masculine noun? Are there any tricks to remember its gender?

German nouns’ genders often must be memorized. However, many masculine nouns share endings like -ig (der König), -ling (der Schmetterling) or denote male persons/roles (der Lehrer). Urlaub doesn’t follow a clear pattern, so the best strategy is to learn it together with its article: der Urlaub.

Why is ist in second position rather than at the end of the sentence?

German main clauses follow the V2 (verb-second) rule: the conjugated verb must occupy the second position. The first position can be the subject, an adverbial phrase, or another element. Here Der Plan für den Urlaub counts as the first element, so ist comes immediately after.