العربي لغة مهمة بالشغل.

Because Arabic usually leaves out is / am / are in the present tense.

So العربي لغة مهمة بالشغل literally looks like:

Arabic — an important language at work

but it naturally means:

Arabic is an important language at work / for work

If you wanted was, will be, and so on, Arabic would use a verb.

In Levantine, languages are often referred to colloquially with the masculine form:

• عربي = Arabic
• إنجليزي = English
• فرنسي = French

So العربي here means Arabic as a language.

العربية is also possible, but it sounds more formal and closer to Modern Standard Arabic. A standard/formal version would more likely use العربية.

Because العربي here is standing on its own as the name of the language, not directly acting as an adjective modifying لغة.

Compare:

• العربي لغة مهمة = Arabic is an important language
• لغة عربية = an Arabic language or more naturally the Arabic language in the right context

In other words, this sentence is not built as one noun phrase Arabic language. It is more like:

• العربي = topic
• لغة مهمة بالشغل = comment about it

Also, مهمة agrees with لغة, not with العربي.

Because in this sentence العربي is being used as a general topic: Arabic as a language in general.

In Levantine, that often sounds natural with الـ when the language is the subject/topic of the sentence.

Compare:

• بحكي عربي = I speak Arabic
• العربي مهم = Arabic is important

Without الـ, عربي often sounds more like an adjective or like the object after a verb such as speak.

Because it is the predicate of the sentence.

Arabic often uses an indefinite noun after the topic/subject in sentences like this:

• العربي لغة مهمة = Arabic is an important language

That is the normal pattern.

If you made لغة definite, the meaning would change or the sentence would sound unnatural in this context.

No. It is not one long noun phrase.

It is better understood as two parts:

• العربي = Arabic
• لغة مهمة بالشغل = an important language at work

So the structure is basically:

Arabic + is + an important language at work

This is why you should not read العربي لغة as if لغة were directly attached to العربي in the same way as لغة عربية.

Because مهمة describes لغة, and لغة is feminine.

In Arabic, adjectives come after the noun and agree with it in:

• gender
• number
• definiteness

So:

• لغة مهمة = an important language
• كتاب مهم = an important book

Here the adjective must be feminine because لغة is feminine.

بالشغل literally contains:

• بـ = a very common preposition that can mean in, at, with, for
• الشغل = work, job, workplace

So here بالشغل most naturally means something like:

• at work
• on the job
• for work
• in a work context

The exact English wording depends on context, but the general idea is in work / for work purposes.

Because in Levantine, بـ is extremely common in everyday speech and often covers meanings that English might express with in, at, or for.

So بالشغل is a very natural colloquial way to say something like:

• at work
• in work
• for work

A more formal version might use في العمل instead.

A careful pronunciation would be something like:

il-ʿarabi luġa muhimme bish-shuġl

In faster everyday Levantine, you may hear something closer to:

l-ʿarabi luġa mhimme bsh-shuġl

A few useful notes:

• ع in العربي has no exact English equivalent
• غ in شغل is a throaty sound, a bit like a French-style r
• in بالشغل, the ل of ال blends into ش, so it sounds like bsh-sh..., not bal-sh...

It is understandable, but it sounds colloquial and Levantine-leaning.

Two big clues are:

• العربي for Arabic
• الشغل for work

A more standard/formal version would be:

العربية لغة مهمة في العمل

So the sentence you have is natural for spoken Levantine, while the formal version would look different.

Yes. That would mean:

Arabic is important at work

That version is shorter and very natural.

The original sentence:

العربي لغة مهمة بالشغل

adds the noun لغة, so it feels a bit fuller:

Arabic is an important language at work

So both work, but the given sentence emphasizes Arabic as a language a little more.