شنطة الظهر تبعي تقيلة.

A natural breakdown is:

• شنطة = bag
• الظهر = the back
• شنطة الظهر = backpack / back bag
• تبعي = my / mine
• تقيلة = heavy

So the sentence is literally something like:

• backpack mine heavy

In natural English, that becomes My backpack is heavy.

Because in Arabic, the present tense of to be is usually omitted.

So instead of saying:

• My backpack is heavy

Levantine Arabic simply says:

• My backpack heavy

This kind of sentence is called a nominal sentence. In the present tense, you normally do not add a verb meaning is/am/are.

This is a noun + noun structure, similar to an iḍāfa construction.

• شنطة الظهر literally means the bag of the back
• idiomatically, it means backpack

In this structure, the first noun usually does not take ال. The second noun can take ال, and that can make the whole phrase definite.

So:

• شنطة الظهر = the backpack / backpack
• not الشنطة الظهر

Because the ة at the end of a feminine noun is often pronounced as -t when the noun is followed by another noun in a linked phrase like this.

So:

• شنطة by itself is often pronounced roughly shanṭa
• شنطة الظهر is often pronounced more like shanṭet eẓ-ẓahr

This is very common in Arabic. The written form stays the same, but the pronunciation changes because the noun is linked to the word after it.

تبعي is a colloquial Levantine way to say mine or my after a noun.

So:

• شنطة الظهر تبعي = my backpack
• literally, the backpack of mine

This is very common in spoken Levantine Arabic. English speakers often expect possession to go before the noun, but in Levantine it is very normal to put this possessive expression after the noun phrase.

That is a very reasonable question.

In many varieties of Levantine, speakers often say:

• تبعي with masculine nouns
• تبعتي with feminine nouns

So some learners might expect:

• شنطة الظهر تبعتي تقيلة

However, actual spoken usage varies by region and by speaker, and you may also hear تبعي used more generally in colloquial speech. So if you have seen تبعي here, it is understandable and natural in many contexts, even if some speakers would personally prefer تبعتي with شنطة.

Because adjectives in Arabic usually agree with the noun they describe.

Here, the main noun is شنطة, and شنطة is feminine, so the adjective must also be feminine:

• تقيل = heavy masculine
• تقيلة = heavy feminine

Since شنطة is feminine, you get:

• شنطة ... تقيلة

Yes, basically.

In Modern Standard Arabic, the word is:

• ثقيلة

In Levantine speech, this is very commonly pronounced and written as:

• تقيلة

Two important colloquial features are happening here:

• ث often becomes ت in everyday speech
• ق may be pronounced differently depending on dialect, often as a glottal stop ء in many urban Levantine accents

So ثقيلة and تقيلة are the same word historically, but تقيلة is the everyday Levantine form.

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

The full noun phrase here is:

• شنطة الظهر تبعي = my backpack

Then the adjective comes after that:

• شنطة الظهر تبعي تقيلة = My backpack is heavy

So the order is basically:

• noun phrase + adjective

That is normal Arabic word order.

Because ظ is a sun letter.

When ال comes before a sun letter, the ل sound is not clearly pronounced, and the following consonant is doubled instead.

So:

• الظهر is written with ال
• but it is pronounced more like eẓ-ẓahr

This is not special to this sentence; it is a general Arabic pronunciation rule.

A reasonable broad Levantine-style pronunciation would be:

• shanṭet eẓ-ẓahr tabaʿi tʔīle

Depending on region, you may hear small differences, especially in:

• the vowel in تبعي
• the pronunciation of ق in تقيلة
• whether a speaker says تبعي or تبعتي

But the overall rhythm is:

• shanṭet eẓ-ẓahr tabaʿi tʔīle

Yes. Some common alternatives are:

• شنطة الظهر تبعتي تقيلة
  Another very natural version, especially if you want feminine agreement with شنطة.

• شنطتي تقيلة
  My bag is heavy. This works if the context already makes it clear you mean your backpack.

• حقيبة الظهر تبعي تقيلة
  More formal-sounding than شنطة.

So the exact form may change a bit, but the original sentence is a very normal colloquial Levantine way to express the idea.