Le poireau est moins cher que l’aubergine aujourd’hui, mais l’aubergine a l’air plus fraîche.

Because French nouns have grammatical gender, and the definite article changes depending on both gender and sound.

• poireau is masculine singular, so it takes le
• aubergine is feminine singular, so normally it would take la

But aubergine begins with a vowel sound, so la becomes l’ by elision:

• la aubergine ❌
• l’aubergine ✅

So:

• le poireau
• l’aubergine

You usually have to learn the gender along with each noun.

In this sentence:

• le poireau tells you poireau is masculine
• l’aubergine by itself does not show gender clearly, but the later adjective fraîche does: it is feminine, so aubergine is feminine

A good habit is to memorize nouns with their article:

• le poireau = leek
• l’aubergine = eggplant / aubergine

This is the standard French pattern for a comparison of less:

• moins + adjective + que
• less + adjective + than

So:

• moins cher que = less expensive than / cheaper than

Examples:

• Ce livre est moins intéressant que l’autre.
• Cette tomate est moins chère que celle-là.

In your sentence:

• Le poireau est moins cher que l’aubergine.

That literally means:

• The leek is less expensive than the eggplant.

No. Moins... que is a comparison, not a negation.

It means:

• less ... than

So:

• Le poireau est moins cher que l’aubergine
  = The leek is less expensive than the eggplant

It is not the same as saying:

• Le poireau n’est pas cher = The leek is not expensive

So even though English sometimes uses not as ... as, French here simply uses moins ... que.

Because cher agrees with poireau, and poireau is masculine singular.

After être, French adjectives agree with the noun they describe:

• le poireau est cher → masculine singular
• l’aubergine est chère → feminine singular

In your sentence, the adjective describes le poireau, so:

• Le poireau est moins cher...

If the subject were feminine, you would write:

• L’aubergine est moins chère que le poireau.

Because fraîche agrees with l’aubergine, which is feminine singular.

The basic adjective is:

• masculine: frais
• feminine: fraîche

So:

• le poireau est frais
• l’aubergine est fraîche

In your sentence:

• l’aubergine a l’air plus fraîche

That means:

• the eggplant looks fresher

The feminine ending changes both the spelling and the pronunciation.

Avoir l’air is a common expression meaning:

• to look
• to seem
• to appear

So:

• l’aubergine a l’air plus fraîche = the eggplant looks fresher = the eggplant seems fresher

Literally, a l’air means has the air, but in normal English you should translate it as looks or seems.

Common pattern:

• avoir l’air + adjective

Examples:

• Il a l’air fatigué. = He looks tired.
• Elle a l’air contente. = She seems happy.

This is called elision. In French, certain short words lose their final vowel before a word that begins with a vowel or silent h.

So:

• le / la → l’
• la aubergine becomes l’aubergine
• le air becomes l’air

This makes pronunciation smoother.

So in your sentence:

• l’aubergine
• a l’air

Note that in a l’air, the l’ belongs to air, not to the verb:

• a = has
• l’air = the look / the appearance, as part of the expression avoir l’air

Aujourd’hui means today, and French adverbs of time are often quite flexible in position.

Here it comes after the comparison:

• Le poireau est moins cher que l’aubergine aujourd’hui

This sounds natural and means that the price comparison is true today.

You could also hear:

• Aujourd’hui, le poireau est moins cher que l’aubergine...

Both are correct. The version in your sentence places the time information after the main comparison.

French often repeats the noun to keep things clear, especially when two different nouns are being compared.

Sentence:

• Le poireau est moins cher que l’aubergine aujourd’hui, mais l’aubergine a l’air plus fraîche.

Repeating l’aubergine avoids ambiguity. If you said:

• ...mais elle a l’air plus fraîche

it would probably still be understood, but the repeated noun is clearer because there are two vegetables in the sentence.

So the repetition sounds natural and helps the listener follow the contrast.

Yes. The adjective must agree with the noun it describes.

Compare:

• Le poireau est moins cher que l’aubergine.
• L’aubergine est moins chère que le poireau.

Same idea, but the adjective changes because the subject changes:

• poireau → masculine → cher
• aubergine → feminine → chère

Yes. In context, plus fraîche means the eggplant seems fresher than the leek, even though que le poireau is not repeated.

French often leaves out the second half of the comparison when it is obvious from context.

Full idea:

• ...mais l’aubergine a l’air plus fraîche
  = ...but the eggplant looks fresher understood as fresher than the leek

If you wanted to make it fully explicit, you could say:

• ...mais l’aubergine a l’air plus fraîche que le poireau.

A simple pronunciation guide is:

luh pwa-roh eh mwan shehr kuh loh-ber-zheen oo-zhoor-dwee, meh loh-ber-zheen ah lehr ploos fresh

A few notes:

• poireau sounds roughly like pwa-roh
• moins sounds like mwan
• cher sounds like shehr
• aubergine sounds roughly like oh-ber-zheen
• fraîche sounds like fresh, but with a French r

Also notice:

• est is usually pronounced eh
• plus fraîche here is usually pronounced with plus sounding like ploos

French often expresses cheap as not expensive or less expensive, rather than using a completely different adjective.

So:

• cher = expensive
• moins cher = less expensive / cheaper
• pas cher = not expensive / cheap

That is very common and natural French.

So:

• Le poireau est moins cher que l’aubergine is a very normal way to say
• The leek is cheaper than the eggplant

It has two main clauses joined by mais:

1. Le poireau est moins cher que l’aubergine aujourd’hui
2. mais l’aubergine a l’air plus fraîche

So the pattern is:

• [subject] + est + comparative adjective + que + [comparison] + [time expression]
• mais + [subject] + a l’air + comparative adjective

This is a useful model for making your own sentences, for example:

• La pomme est moins chère que la poire aujourd’hui, mais la poire a l’air plus mûre.
• Le café est moins fort que le thé, mais le thé a l’air plus chaud.