هذه ليلة جميلة.

Because ليلة is a feminine singular noun, and the demonstrative this must match it in gender.

• هذا = this for masculine singular
• هذه = this for feminine singular

So with ليلة (night), you use هذه.

In Arabic, the verb to be in the present tense is usually not expressed.

So:

• هذه ليلة جميلة literally looks like this a night beautiful
• but naturally means This is a beautiful night

This kind of sentence is called a nominal sentence in Arabic.

If you wanted was or will be, Arabic would normally use a verb, but for simple present-tense statements, Arabic usually leaves is/am/are out.

A simple way to understand it is:

• هذه = this
• ليلة = night
• جميلة = beautiful

Grammatically:

• هذه is the topic or starting point of the sentence
• ليلة is the predicate: it tells you what this is
• جميلة describes ليلة

So the structure is basically:

this + night + beautiful
= This is a beautiful night

Because in Arabic, adjectives normally come after the noun they describe.

So:

• ليلة جميلة = a beautiful night
  • literally: night beautiful

This is the normal Arabic word order for noun + adjective.

Because the adjective must agree with the noun it describes.

Since ليلة is feminine singular, the adjective must also be feminine singular:

• جميل = beautiful (masculine)
• جميلة = beautiful (feminine)

So:

• ليل جميل = a beautiful night/evening if the noun were masculine
• ليلة جميلة = a beautiful night

Arabic adjectives agree with nouns in:

• gender
• number
• definiteness
• case

That final ة is called taa marbuuTa.

It often marks a word as feminine, especially in singular nouns and adjectives.

So here:

• ليلة is a feminine noun
• جميلة is a feminine adjective matching it

In pause, ة is usually pronounced like -a or -ah:

• ليلة ≈ laylah
• جميلة ≈ jamīlah

But in some grammatical contexts, it can sound like -t when endings are fully pronounced.

Because the phrase means a beautiful night, not the beautiful night.

In Arabic:

• ليلة جميلة = a beautiful night (indefinite)
• الليلة الجميلة = the beautiful night (definite)

Since ليلة is indefinite here, جميلة must also be indefinite. Adjectives in Arabic match the noun in definiteness too.

So:

• هذه ليلة جميلة = This is a beautiful night
• هذه الليلة الجميلة usually means this beautiful night

That second version is no longer the same structure or meaning.

They are similar, but not identical.

• هذه ليلة جميلة = This is a beautiful night

  • ليلة is indefinite: a night

• هذه الليلة جميلة = This night is beautiful or Tonight is beautiful

  • الليلة is definite: the night / this night

So the first sentence identifies what this is.
The second talks about a specific night and says something about it.

It would usually be written as:

هٰذِهِ لَيْلَةٌ جَمِيلَةٌ

Those final -un endings show the nominative case in fully vowelled formal Arabic:

• ليلةٌ
• جميلةٌ

In normal everyday writing, these short vowels are usually omitted, so you normally see:

هذه ليلة جميلة

In spoken Arabic and in pausal reading, the full case endings are often not pronounced.

A careful MSA pronunciation is approximately:

hādhihi laylatun jamīlatun

In a more paused or simplified pronunciation, you may hear something closer to:

hādhihi layla jamīla(h)

A few pronunciation notes:

• ذ in هذه sounds like th in this
• ليلة is roughly LAY-la(h)
• جميلة is roughly ja-MEE-la(h)

So an English-friendly approximation is:

HAA-dhi-hi LAY-la ja-MEE-la

Sometimes Arabic word order is flexible, but changing it can change the emphasis or even the meaning.

For this exact basic sentence, هذه ليلة جميلة is the normal, straightforward version.

If you change it to something like هذه الليلة جميلة, that is not just a word-order change — it also changes the definiteness and meaning to This night is beautiful.

So for learners, the safest choice is to keep:

هذه ليلة جميلة

as the standard way to say This is a beautiful night.