في هذا الشهر لدينا اجتماع مهم في الشركة.

Yes. Both are possible, but they are slightly different in style.

• في هذا الشهر literally means in this month
• هذا الشهر means this month

In Arabic, time expressions are often introduced with في when you want to make the time setting explicit. So في هذا الشهر لدينا... is very natural and clear in MSA.

A shorter version, هذا الشهر لدينا اجتماع مهم في الشركة, is also possible and would still mean This month, we have an important meeting at the company.

لدينا means we have, but literally it is closer to with us or at our disposal.

It is made from:

• لدى = a formal word meaning with / in the possession of
• نا = us / we

So:

• لديّ = I have
• لديك = you have
• لدينا = we have

Arabic often expresses possession this way rather than with a separate verb meaning to have.

In Arabic, possession is usually not expressed with a verb like English have.

Instead, Arabic commonly uses a structure meaning something like:

• at us is...
• with us is...

So لدينا اجتماع مهم literally works like:

• With us there is an important meeting

But the natural English translation is:

• We have an important meeting

This is a very common pattern in Arabic.

After a demonstrative like هذا (this), the noun is normally definite in MSA. So Arabic says:

• هذا الشهر = this month

not:

• هذا شهر

This is different from English. In Arabic, both parts help show definiteness:

• هذا = this
• الشهر = the month

So literally it is closer to this the-month, though of course you should understand it simply as this month.

Because شهر is a masculine noun.

In Arabic, demonstratives must agree with the noun in gender:

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

So:

• هذا الشهر = this month
• هذه الشركة = this company

Since شهر is masculine, هذا is correct.

اجتماع is indefinite because the sentence is presenting an important meeting, not pointing to a specific already-known meeting.

So:

• اجتماع مهم = an important meeting
• الاجتماع المهم = the important meeting

If the speaker and listener already knew which meeting was meant, الاجتماع could be used. But in this sentence, the indefinite form sounds natural.

In Arabic, adjectives normally come after the noun they describe.

So:

• اجتماع مهم = an important meeting

not the other way around.

This is the normal Arabic order:

• noun + adjective

Also, the adjective must match the noun in:

• gender
• number
• definiteness
• case

Here both are:

• masculine
• singular
• indefinite

So اجتماع مهم is a correct match.

Because the adjective must match the noun in definiteness.

Since the noun is indefinite:

• اجتماع = a meeting

the adjective must also be indefinite:

• مهم = important

So:

• اجتماع مهم = an important meeting

If the noun were definite, the adjective would also be definite:

• الاجتماع المهم = the important meeting

This matching rule is very important in Arabic.

It can be understood as at the company or in the company, depending on context.

• في often means in
• but with places, it can also be translated naturally as at

So في الشركة could suggest:

• the meeting happens at the company
• the meeting is within the company setting

In English, at the company is often the most natural translation here.

Yes. You could say:

• في هذا الشهر عندنا اجتماع مهم في الشركة

This would also mean This month we have an important meeting at the company.

The difference is mostly one of style:

• لدينا is often felt to be more formal or more typical of written MSA
• عندنا is very common and natural too, especially in everyday use

Both are correct.

It would be:

فِي هَذَا الشَّهْرِ لَدَيْنَا اجْتِمَاعٌ مُهِمٌّ فِي الشَّرِكَةِ

A few notes:

• الشهرِ is genitive because it comes after في
• اجتماعٌ is nominative in this kind of there is / we have structure
• مهمٌّ matches اجتماعٌ, so it is also nominative
• الشركةِ is genitive because it also comes after في

Learners often first meet Arabic without case endings in normal print, but this is the full grammatical form.

Because ش is a sun letter.

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

So:

• الشهر is pronounced roughly ash-shahr
• الشركة is pronounced roughly ash-sharika

The spelling still keeps ال, but the pronunciation changes.

This is a very common pronunciation rule in Arabic.

Grammatically, it is a kind of existential or possession structure.

A simple way to understand it is:

• لدينا = we have / with us
• اجتماع مهم = an important meeting

So the whole phrase means:

• We have an important meeting

In more traditional grammar terms, لدينا functions like a fronted phrase, and اجتماع is the noun that follows it. But for a learner, the most useful takeaway is simply that:

• لدى + pronoun is a common way to say have

Yes, Arabic word order is fairly flexible.

The given sentence:

في هذا الشهر لدينا اجتماع مهم في الشركة

is natural and emphasizes the time frame first: this month.

Other possible orders include:

• لدينا اجتماع مهم في الشركة في هذا الشهر
• اجتماع مهم لدينا في الشركة في هذا الشهر

But not all versions sound equally natural in every context. The original sentence is a good, clear MSA choice because it introduces the time first, then the main information.