هذا الخط جديد.

A common full reading is hādhā al-khaṭṭu jadīdun.

A few pronunciation notes:

• خ in الخط is like the ch in Scottish loch or German Bach, not like English k or h.
• ط is an emphatic t sound.
• The ّ on ط means the consonant is doubled: khaṭ-ṭ.
• In everyday reading aloud, final case endings are often dropped in pause, so you may also hear something like hādhā al-khaṭṭ jadīd.

In Arabic, the verb to be is usually omitted in the present tense.

So:

• هذا الخط جديد = This line/script is new

But in other tenses, Arabic does use a verb:

• كان هذا الخط جديدًا = This line/script was new

This type of sentence, with no present-tense is, is very common in Arabic.

In Modern Standard Arabic, when a demonstrative like هذا is followed by a noun, that noun is normally definite, so it usually takes الـ.

So Arabic says:

• هذا الخط

Literally, this is something like this the-line, but the natural English meaning is just this line/script.

That is normal Arabic structure.

Because الخط is a masculine singular noun, and the demonstrative has to match it.

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

So:

• هذا الخط = this line/script because خط is masculine

If the noun were feminine, you would use هذه instead.

Because the adjective must agree with the noun in gender and number.

• الخط is masculine singular
• so the adjective is also masculine singular: جديد

If the noun were feminine singular, the adjective would normally be جديدة.

Not here. In this sentence, جديد is the predicate: it is telling you something about هذا الخط.

So:

• هذا الخط جديد = This line/script is new

In this kind of sentence, the predicate adjective is usually indefinite, so it does not take الـ.

Compare:

• هذا الخط جديد = This line is new
• الخط الجديد = the new line/script

So جديد and الجديد are not doing the same job.

They are different structures:

• هذا الخط جديد is a full sentence: This line/script is new
• الخط الجديد is just a noun phrase: the new line/script

A useful way to see it:

• جديد by itself here means is new
• الجديد after the noun means new as a describing adjective inside the noun phrase

الخط has a wider range of meanings than just one English word.

Depending on context, it can mean:

• line
• handwriting
• script
• font
• calligraphy
• sometimes even a line in a broader or technical sense

So the exact translation depends on what the speaker is talking about. In a design or calligraphy context, الخط often means script, font, or handwriting style.

Most normal Arabic writing leaves out short vowels and case endings.

So you usually see:

• هذا الخط جديد

But a fully vocalized reading would be something like:

• hādhā al-khaṭṭu jadīdun

Those endings help show grammar, but in everyday print they are usually not written, especially in texts for native readers.

Because the word itself contains a doubled consonant: خَطّ.

That doubling is shown by the shadda mark: ّ.

So:

• خط is pronounced roughly khaṭṭ, not khaṭ

Also, this doubling is part of the word itself. It is not caused by الـ. The article in الخط is pronounced normally here because خ is not one of the letters that causes assimilation of الـ.