Learn Hardcore French: Les fraises du marché sont chères, mais leur goût est magnifique. - The strawberries from the market are expensive, but their taste is wonderful.

In French, you cannot say de le marché; the language always contracts de le to du. So les fraises du marché is the strawberries from the market.

Why is it les fraises du marché and not just fraises du marché?

French usually needs an article in front of a noun, even when English does not.

les fraises = the strawberries
Dropping the article (∅ fraises du marché) is normally wrong in standard French (outside of some titles, lists, or telegram style).

So to talk about these strawberries in a normal sentence, you say les fraises du marché.

Why is it chères and not cher in les fraises du marché sont chères?

Adjectives in French agree in gender and number with the noun.

une fraise is feminine singular
les fraises is feminine plural

The base adjective is cher (expensive).
Its forms are:

masculine singular: cher
feminine singular: chère
masculine plural: chers
feminine plural: chères

Since les fraises is feminine plural, you must use chères.

Why does chères have an accent grave (è)?

The accent changes both spelling and pronunciation:

cher: e is pronounced like é (closed sound, similar to ay in day but shorter)
chère / chères: è is an open e sound (more like e in bed).

Feminine forms are written chère / chères with è, not chere / cheres.
So chères is the correct feminine plural spelling.

Why does the sentence not say sont chères something (like sont chères les fraises) as in English are expensive?

In French, être + adjective is enough:

Les fraises sont chères. = The strawberries are expensive.

You do not add an extra word like are expensive ones.
The structure subject + être + adjective already makes a complete predicate.

Why is it leur goût and not leurs goûts or son goût?

Leur here is a possessive determiner meaning their.

leur is used when the possessed thing is singular, even if the owners are plural
leurs is used when the possessed things are plural

Here, the strawberries (plural owners) have one overall flavor:

owners plural, thing singular → leur goût = their taste / flavor

You could say leurs goûts if you really meant several different tastes, but normally for food you talk about its overall flavor, so you keep goût singular and use leur.

Son goût would mean its taste / his taste / her taste, referring to a single owner, not to the strawberries as a group.

Why is goût singular when we are talking about several strawberries?

French often uses a singular noun when talking about a general quality shared by a plural subject.

The idea is: The strawberries’ flavor (as a whole) is magnificent, not each individual strawberry has its own separate taste.

So:

Les fraises sont bonnes. → plural adjective for the berries themselves
Leur goût est magnifique. → singular goût for the overall flavor they have.

Why is it magnifique and not magnifiques?

Magnifique is an adjective that agrees with the noun it describes.
Here, it describes goût, which is:

le goût → masculine singular

So the adjective must be masculine singular too:

un goût magnifique
leur goût est magnifique

If the noun were plural (for example leurs goûts), you would write magnifiques.

Can I say délicieux instead of magnifique? Would the grammar change?

Yes, you can; the meaning shifts slightly but the grammar follows the same rules of agreement.

délicieux (delicious) is masculine singular and masculine plural
délicieuse / délicieuses are the feminine forms

Since goût is masculine singular, you would say:

Leur goût est délicieux.

Only the adjective changes; the structure of the sentence stays the same.

How do you pronounce the sentence Les fraises du marché sont chères, mais leur goût est magnifique?

Approximate pronunciation (French-style IPA, then a rough English guide):

Les fraises du marché → /le fʁɛz dy maʁʃe/
- les → lay
- fraises → frehz (final s = z sound)
- du → dy (like dü)
- marché → mar-shay
sont chères → /sɔ̃ ʃɛʁ/
- sont → nasal sohn (the t is silent here)
- chères → shair (final s silent)
mais → /mɛ/ → meh
leur goût est magnifique → /lœʁ ɡu ɛ maɲifik/
- leur → between lur and lœr
- goût → goo (final t silent, the û lengthens the sound a bit)
- est → eh (here the t is silent)
- magnifique → ma-nyi-feek

Spoken smoothly, you get something like:
Leh frehz dü mar-shay sohn shair, meh lur goo eh ma-nyi-feek.

Could you change the order and say leur goût magnifique est…?

You can say leur magnifique goût or leur goût magnifique, but the meaning changes slightly:

leur goût est magnifique: you are making a statement about their taste (their taste is magnificent).
leur magnifique goût: you are describing the noun more compactly (their magnificent taste), usually as part of a larger sentence.

For example:

Les fraises du marché sont chères, mais leur magnifique goût me plaît beaucoup.
→ …but their magnificent taste pleases me a lot.

In the original sentence, leur goût est magnifique is the most natural way to make a clear, direct comment about the taste.