O cliente está satisfeito com o jantar.

O is the masculine singular definite article in Portuguese, equivalent to the in English.

• O cliente = the customer / the client
• Cliente on its own would sound like just saying customer without the, which is usually odd here.

In this specific sentence, you are talking about a particular customer, so you normally must use the article: O cliente está satisfeito…

You can drop the article in headlines or notes (e.g. on a restaurant ticket), but in normal speech O is expected.

Portuguese uses:

• estar for temporary states or conditions
• ser for permanent or defining characteristics

Being satisfied with a particular dinner is a temporary state, so you use estar:

• O cliente está satisfeito com o jantar.
  The client is (currently) satisfied with the dinner.

If you said O cliente é satisfeito, it would sound like he is a satisfied person in general (as a character trait), and even then it is not a very usual phrasing in European Portuguese. For this meaning, está satisfeito is the natural choice.

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

• cliente can be masculine or feminine:
  • o cliente (male customer)
  • a cliente (female customer)

The adjective satisfeito changes to match:

• Male customer:
  O cliente está satisfeito com o jantar.
• Female customer:
  A cliente está satisfeita com o jantar.

Plurals:

• Male or mixed group: Os clientes estão satisfeitos…
• All female group: As clientes estão satisfeitas…

In Portuguese, certain adjectives naturally take specific prepositions. With satisfeito, the normal preposition for the thing you are satisfied about is com:

• estar satisfeito com algo = to be satisfied with something

So:

• O cliente está satisfeito com o jantar.
  The client is satisfied with the dinner.

Using de (satisfeito de) for this meaning is not standard in European Portuguese; com is the natural choice here.

In standard written Portuguese, the preposition com does not contract with the definite article o:

• com + o = com o
• com + a = com a
• com + os = com os
• com + as = com as

So com o jantar is exactly the correct standard form.

In fast, informal speech, Portuguese speakers may pronounce com o jantar in a reduced way (sounding a bit like c’mo jantar), but in writing it stays com o.

Portuguese normally uses the definite article with specific, concrete things:

• com o jantar = with the dinner (the particular dinner we are talking about)

You can say com jantar in some special contexts (e.g. a menu description: Quarto com jantar incluído – room with dinner included), but when you are talking about a specific event tonight, com o jantar is the natural form.

So for this sentence, com o jantar is the idiomatic choice.

The normal, neutral word order is:

• [Subject] O cliente
• [Verb] está
• [Complement] satisfeito com o jantar

→ O cliente está satisfeito com o jantar.

Other orders are possible but sound marked, heavy, or poetic:

• Está o cliente satisfeito com o jantar.
  Very formal / literary, with emphasis on está.
• O cliente está, com o jantar, satisfeito.
  Stylistic, maybe in written emphasis.

O cliente com o jantar está satisfeito is not wrong grammatically, but it sounds awkward and unnatural in everyday European Portuguese. Stick to O cliente está satisfeito com o jantar.

Cliente covers both senses:

• Someone who pays for a product or service in a restaurant, shop, hotel, etc. → customer
• Someone who pays a professional like a lawyer, architect, or consultant → client

In a restaurant in Portugal, staff will naturally refer to diners as clientes:

• Os clientes estão satisfeitos?
  Are the customers satisfied?

You need to put everything in the plural:

• O cliente → Os clientes
• está → estão (3rd person plural of estar)
• satisfeito → satisfeitos (masculine plural)

So:

• Os clientes estão satisfeitos com o jantar.

If all the customers are female:

• As clientes estão satisfeitas com o jantar.

Jantar is both a noun and a verb:

1. Noun – o jantar = the dinner

   • O jantar está pronto. – The dinner is ready.

2. Verb – jantar = to have dinner / to dine

   • Vamos jantar às oito. – We are going to have dinner at eight.

In O cliente está satisfeito com o jantar, jantar is clearly a noun because it has the article o before it.

Very roughly (European Portuguese):

• O → like oo in food, short: [u]
• cliente → [kli-ÉN-tɨ] (final -e is a weak sound, like a very short uh)
• está → [ʃ-TA] (initial e is almost swallowed; tá stressed)
• satisfeito → [sɐ-tiʃ-FÊI-tu]
  
  • s in satis like English s
  • feito similar to fay-too
• com → [kõ], with nasal om (like French bon)
• o → again [u]
• jantar → [ʒɐn-TAR]
  
  • j like the s in measure
  • final r is soft or almost not pronounced in much of Portugal

All together, something like:

• [u kliˈẽtɨ ʃˈta sɐtiʃˈfejtu kõ u ʒɐ̃ˈtaɾ]

The main stresses are on -en- in cliente, -tá in está, -fei- in satisfeito, and -tar in jantar.

Yes:

• O cliente está satisfeito com o jantar.
• Ele está satisfeito com o jantar. – He is satisfied with the dinner.

In Portuguese you can often drop subject pronouns when the subject is clear from context:

• Está satisfeito com o jantar.
  Literally: Is satisfied with the dinner.

This would normally be understood as He is satisfied with the dinner, if you were already talking about o cliente or ele just before it.

Yes, you can say:

• O cliente está contente com o jantar.

Both satisfeito and contente often translate as happy / satisfied, but there is a nuance:

• satisfeito – more about being satisfied, having expectations met, feeling that the quality/quantity was good.
• contente – more about being glad / pleased / happy emotionally.

In a restaurant context, está satisfeito com o jantar is very common and slightly more focused on the food and service meeting expectations. Está contente com o jantar sounds a bit more like he is simply happy with it.