La meva mare diu que aquesta idea és bona.

In Catalan, it is very common to use the definite article before a possessive with family members and many everyday nouns.

So la meva mare literally looks like the my mother, but in normal Catalan it simply means my mother.

This is different from English, where you normally do not say the my mother.

Some common examples:

• el meu pare = my father
• la meva germana = my sister
• el meu cotxe = my car

So la meva mare is the normal Catalan pattern.

Catalan possessives usually come before the noun, just like in English.

• la meva mare = my mother
• aquesta idea = this idea

Putting the possessive after the noun is much less common and usually sounds more literary, emphatic, or restricted to certain contexts. For a learner, the normal order to use is:

• article + possessive + noun

So:

• la meva mare
• el meu amic
• les seves idees

Diu is the third person singular present tense of the verb dir, which means to say.

So:

• jo dic = I say
• tu dius = you say
• ell/ella diu = he/she says

In this sentence, the subject is la meva mare, which is she, so Catalan uses diu:

• La meva mare diu... = My mother says...

Here, que means that and introduces the clause after diu.

• La meva mare diu que... = My mother says that...

In English, that is often optional:

• My mother says this idea is good
• My mother says that this idea is good

In Catalan, que is normally used in this structure, so it is much less natural to leave it out.

Aquesta means this and agrees with idea, which is a feminine singular noun.

Catalan demonstratives agree in gender and number with the noun:

• aquest = this, masculine singular
• aquesta = this, feminine singular
• aquests = these, masculine plural
• aquestes = these, feminine plural

Since idea is feminine singular, you need aquesta:

• aquesta idea = this idea

Because Catalan treats idea as a feminine noun, so it takes feminine words with it.

You can see this in two places:

• aquesta idea
• és bona

Both aquesta and bona are feminine singular, matching idea.

Many nouns ending in -a are feminine, though not all, so agreement is a very useful clue.

Because adjectives in Catalan usually agree with the noun they describe in gender and number.

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

• masculine singular: bo
• feminine singular: bona
• masculine plural: bons
• feminine plural: bones

So:

• un llibre bo = a good book
• una idea bona or more naturally una bona idea = a good idea

In your sentence:

• aquesta idea és bona = this idea is good

Catalan often distinguishes between ser and estar, somewhat like Spanish.

Here, és is from ser, and it is used because bona describes a quality or judgment about the idea.

• aquesta idea és bona = this idea is good

You would not normally use estar here. Estar is more often used for states, conditions, or location in many contexts.

So for a general evaluation like good, interesting, important, Catalan often uses ser:

• És interessant
• És important
• És bona

The sentence follows a very common Catalan pattern:

• La meva mare = subject
• diu = verb
• que aquesta idea és bona = subordinate clause

Inside the second clause:

• aquesta idea = subject
• és = verb
• bona = adjective/complement

So the structure is basically:

Subject + verb + que + subject + verb + complement

This is quite similar to English:

• My mother says that this idea is good

Yes, but it is usually unnecessary.

Catalan is a language that often drops subject pronouns because the verb form already tells you the person.

So:

• La meva mare diu... is perfectly complete
• Ella diu... is also possible, but only if you want emphasis, contrast, or clarification

For example:

• La meva mare diu que aquesta idea és bona is the natural neutral sentence.

The accent in és helps distinguish it from other words and also shows stress.

• és = is
• es = an unstressed pronoun, like oneself / himself / herself / itself, depending on context

So the accent is important because it marks a different word.

Examples:

• És bona = It is good
• Es diu Marta = She is called Marta

Diu is usually pronounced roughly like dee-oo said quickly as one syllable or very tightly connected.

A simple learner-friendly approximation is:

• diu ≈ dyoo

The d is soft, and the iu combination glides together.

If you are aiming for a practical pronunciation:

• La meva mare diu ≈ la MEH-va MA-re dyoo

Exact pronunciation varies somewhat across Catalan varieties, but that approximation is good for a learner.

Usually no, or at least not in normal standard usage.

English often says:

• My mother says this idea is good

But Catalan normally keeps que:

• La meva mare diu que aquesta idea és bona

For learners, the safest rule is: after verbs like dir, pensar, creure, use que before the next clause.

Yes. That would mean My mother says that this idea is very good.

You are just adding molt = very before the adjective:

• bona = good
• molt bona = very good

This is a very natural expansion of the same sentence pattern.