الحقيقة مهمة.

In Arabic, the present-tense to be is usually left out.

So الحقيقة مهمة literally looks like the truth important, but it means The truth is important.

This is completely normal in both Standard Arabic and Levantine.
If you wanted past or future, then Arabic would use other words, for example:

• الحقيقة كانت مهمة = The truth was important
• الحقيقة بتكون مهمة = The truth will be important / is going to be important in Levantine

Because الحقيقة is the subject and it is definite: the truth.

The word مهمة is the predicate adjective: important. In Arabic, when an adjective comes after a noun inside a noun phrase, it matches definiteness. But here مهمة is not modifying الحقيقة as part of one noun phrase; it is telling you something about الحقيقة.

So:

• الحقيقة المهمة = the important truth
  Here المهمة would also need الـ because it is a true adjective modifying the noun.

But:

• الحقيقة مهمة = the truth is important
  Here مهمة is the predicate, so it stays indefinite.

Because الحقيقة is a feminine noun, and Arabic adjectives agree with the noun in gender.

So:

• الحقيقة مهمة = feminine noun + feminine adjective

If the noun were masculine, you would use the masculine form:

• الكتاب مهم = the book is important

This agreement is very important in Arabic.

A big clue is the ending ـة (called taa marbuuTa). Very often, nouns ending in ـة are feminine.

So حقيقة is feminine, and that is why the adjective becomes مهمة.

Not every feminine noun ends this way, and not every word ending this way behaves simply in all contexts, but it is a very strong pattern and a good beginner clue.

A common Levantine-style pronunciation would be:

il-ḥaʔīʔa mhimme
or
el-ḥaʔīʔa mhimme

A few things to notice:

• الـ is often pronounced il- or el-
• ق in many Levantine dialects becomes a glottal stop ʔ, so حقيقة sounds like ḥaʔīʔa
• مهمة in Levantine is often mhimme, not the more careful Standard Arabic-style muhimma

So the written sentence is the same, but the spoken pronunciation is more dialectal.

Levantine often shortens vowels in everyday speech.

So the Standard Arabic form muhimma becomes something like mhimme in Levantine pronunciation.

This is very common in dialects: the spelling may look Standard, but the actual pronunciation is more compressed and conversational.

So:

• Writing: مهمة
• Levantine pronunciation: mhimme

Not if you mean the truth is important.

Because الحقيقة is feminine, the adjective should also be feminine:

• correct: الحقيقة مهمة
• not correct here: الحقيقة مهم

You would use مهم with a masculine noun, like:

• الموضوع مهم = the topic is important

The writing works perfectly in Standard Arabic, and it also works fine in Levantine writing.

What changes most in Levantine is the pronunciation, not the basic structure of this sentence.

So:

• as written, الحقيقة مهمة is natural and clear
• in spoken Levantine, it would usually be pronounced more like il-ḥaʔīʔa mhimme

This is one of those sentences where Standard Arabic and Levantine are very close.

A very common Levantine negation would be:

الحقيقة مو مهمة = The truth is not important

Here مو is a very common Levantine way to say not with adjectives and nouns.

You may also hear:

• الحقيقة مش مهمة

Both are common in different areas and speaking styles.

The most normal order is:

الحقيقة مهمة

That is the clearest, most neutral way to say The truth is important.

Arabic can sometimes change word order for emphasis, but for a learner, this standard order is the best one to use first:

• subject: الحقيقة
• predicate adjective: مهمة

So yes, Arabic can be flexible, but this sentence is already in the most straightforward order.

In fully vowelled Standard Arabic, it would be:

الحقيقةُ مهمّةٌ

Those final short vowels show grammatical case in Standard Arabic:

• الحقيقةُ = nominative subject
• مهمّةٌ = nominative predicate

In everyday Levantine, these case endings are not used in speech, and they are usually not written either. That is why learners normally see the simpler written form:

الحقيقة مهمة