النت في البيت بطيء النهارده.

A natural Egyptian pronunciation would be:

en-net fil-bēt ba-teeʔ en-naharda

A few notes:

• النت → en-net
• في البيت is usually said together as fil-bēt
• بطيء → ba-teeʔ
  The last sound is a light glottal stop, like a small catch in the throat.
• النهارده → en-naharda

So the whole sentence flows pretty smoothly as:

en-net fil-bēt ba-teeʔ en-naharda

This is because of the sun-letter / moon-letter rule.

• In النت, the word starts with ن, which is a sun letter, so the ل in ال is not pronounced.
  So النت sounds like en-net, not el-net.

• In البيت, the word starts with ب, which is a moon letter, so the ل is pronounced.
  So البيت sounds like el-bēt.

The same thing happens in النهارده:

• ن is a sun letter
• so it is pronounced en-naharda

Here is a simple breakdown:

• النت = the internet / the net
• في البيت = at home / in the house
• بطيء = slow
• النهارده = today

So literally, it is something like:

The internet at home slow today.

That sounds incomplete in English, but in Arabic this is a normal full sentence.

In Arabic, especially in the present tense, you usually do not say a word for is / am / are.

So:

• النت بطيء = The internet is slow
• literally: The internet slow

This is a very common Arabic pattern called a nominal sentence.

If you wanted a past meaning, then you would use a verb such as كان:

• النت كان بطيء = The internet was slow

But in the present, no is is needed.

In Egyptian Arabic, في البيت literally means in the house, but it is also very commonly used to mean at home.

So in everyday speech:

• أنا في البيت = I’m at home
• النت في البيت بطيء = The internet at home is slow

As for البيت having ال, that is normal. Arabic often says the house where English would simply say home.

So في البيت is one of the standard ways to express at home.

النت is a very common Egyptian colloquial borrowing from the English word net, meaning the internet.

It is extremely common in speech.

You may also hear:

• الإنترنت = the internet

The difference is mostly style:

• النت = more everyday, casual, very common in speech
• الإنترنت = a bit more formal or full-sounding

So this sentence sounds natural and conversational because it uses النت.

Because بطيء here is the predicate of the sentence: it tells you something about النت.

In Arabic, in this kind of sentence, the pattern is often:

• definite noun + indefinite adjective/predicate

So:

• النت بطيء = The internet is slow

But:

• النت البطيء = the slow internet

That second one is not a full sentence. It is just a noun phrase.

So:

• النت بطيء = statement
• النت البطيء = description of a noun

Because النت is treated as a masculine singular noun here, so the adjective matches it.

That is why you get:

• النت بطيء

If the noun were feminine, the adjective would usually be feminine too:

• العربية بطيئة = The car is slow

So the form بطيء matches the gender of النت.

Yes. النهارده is a very common Egyptian Arabic word meaning today.

It is colloquial Egyptian, not formal Modern Standard Arabic.

A rough comparison:

• Egyptian Arabic: النهارده
• Modern Standard Arabic: اليوم

Historically, النهارده comes from something like this day, and that is why it has that shape.

So this sentence sounds clearly Egyptian because of النهارده.

Yes, the word order can change, but the version you have is very natural.

In Egyptian Arabic, time expressions like النهارده often come at the end:

• النت في البيت بطيء النهارده

This sounds like a normal everyday statement:
The internet at home is slow today.

You could move things around for emphasis, for example:

• النهارده النت في البيت بطيء
  = Today, the internet at home is slow

That is possible, but the original sentence is the most neutral and natural way to say it.

It is definitely spoken Egyptian Arabic.

The clearest signs are:

• النت instead of the more formal الإنترنت
• النهارده instead of formal اليوم

A more formal version would be something like:

• الإنترنت في البيت بطيء اليوم

So if you say النت في البيت بطيء النهارده, you sound natural and conversational in Egyptian Arabic.