هذه خطة جيدة.

Because خطة is a feminine noun in Arabic, and the demonstrative has to match it.

• هذا = this for masculine nouns
• هذه = this for feminine nouns

So:

• هذا كتاب = This is a book
• هذه خطة = This is a plan

Even though English uses just this for both, Arabic makes this gender distinction.

A very common clue is the ة at the end, called taaʾ marbuuṭa. Many nouns ending in ة are feminine.

So خطة is feminine, which is why it takes:

• هذه instead of هذا
• جيدة instead of جيد

This pattern is extremely common in Arabic.

In Arabic, the verb to be is usually not expressed in the present tense in simple sentences like this.

So:

• هذه خطة جيدة literally looks like This plan good
• but it means This is a good plan

This kind of sentence is called a nominal sentence.

If you wanted a past or future meaning, Arabic would use a form of كان or another verb, but in the present tense, the is/am/are is normally omitted.

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

So:

• خطة جيدة = a good plan
• literally: plan good

This is the normal word order for noun + adjective in Arabic.

Because Arabic adjectives must agree with the noun they describe.

Since خطة is feminine singular, the adjective must also be feminine singular:

• masculine: جيد
• feminine: جيدة

So:

• كتاب جيد = a good book
• خطة جيدة = a good plan

This agreement is one of the most important features of Arabic grammar.

Great question. In هذه خطة جيدة, the structure is a full sentence:

• هذه = this
• خطة جيدة = a good plan

So the meaning is This is a good plan, not this good plan.

That is why خطة is indefinite here.

Compare:

• هذه خطة جيدة = This is a good plan
• هذه الخطة الجيدة = this good plan

In the second example, الخطة الجيدة is a definite noun phrase, and both the noun and adjective take الـ.

It is a sentence.

More specifically, it is a nominal sentence made of:

• هذه = the topic / subject-like element
• خطة جيدة = the predicate / comment about it

So the sentence means:

• This is a good plan

If you wanted a noun phrase meaning this good plan, you would normally say:

• هذه الخطة الجيدة

That difference is very important.

Demonstratives like هذا and هذه are generally treated as fixed forms in normal usage. They do not show the same visible case ending patterns that many regular nouns do.

So in this sentence, هذه stays هذه.

The noun and adjective can have case endings in fully vocalized formal Arabic, but in ordinary writing those endings are usually left unwritten.

In fully vocalized, formal MSA, it could be written:

هٰذِهِ خُطَّةٌ جَيِّدَةٌ

This reflects the normal nominative ending for the predicate phrase in this kind of sentence.

But in everyday printed Arabic, you will almost always see:

هذه خطة جيدة

without the short vowels and nunation written out.

It is pronounced approximately khuṭṭa.

A few important notes:

• خ is a throaty kh sound, like the ch in German Bach or Scottish loch
• ط is an emphatic t
• the طّ means the consonant is doubled, so you hold it slightly longer
• the final ة is pronounced like a in pause: khuṭṭa

So the whole word is roughly:

khuṭ-ṭa

It is usually pronounced approximately jayyida.

Helpful breakdown:

• ج in MSA is commonly taught as j as in jam
• يّ gives a doubled y sound
• the ending ة is pronounced a when pausing

So:

جَيِّدَة → jayyida

In careful grammar discussion, you may also hear case endings added in full reading, but in normal pause it is simply jayyida.

Because Arabic adjectives match the noun in definiteness as well as gender and number.

Since خطة is indefinite, جيدة must also be indefinite.

Compare:

• خطة جيدة = a good plan
  both indefinite

• الخطة الجيدة = the good plan
  both definite

This matching rule is very consistent in Arabic.

Yes, but it means something different.

• هذه خطة جيدة = This is a good plan
• الخطة جيدة = The plan is good

So both are correct, but they are not interchangeable.

The first points to something: this The second talks about a specific known plan: the plan

The standard, natural order is:

هذه خطة جيدة

That is the normal way to say This is a good plan.

Arabic does allow some variation in word order for emphasis in some contexts, but for a learner, this is the best and most straightforward pattern to use.

A very useful pattern is:

هذه + noun + adjective

for feminine nouns, meaning:

This is a/an [adjective] [noun].

Examples:

• هذه سيارة جديدة = This is a new car
• هذه فكرة ممتازة = This is an excellent idea
• هذه قصة طويلة = This is a long story

For masculine nouns, use:

هذا + noun + adjective

For example:

• هذا كتاب مفيد = This is a useful book