Learn Hardcore Romanian: Dacă ești liber mâine, hai să mergem la restaurantul ieftin. - If you are free tomorrow, let's go to the cheap restaurant.

In Romanian, when a condition refers to the future, you normally use the simple present in both the dacă-clause and the main clause. So Dacă ești liber mâine literally means If you are free tomorrow, even though it talks about the future. Using Dacă vei fi liber mâine isn’t wrong, but it sounds more formal or marked; everyday speech favors the simple present.

What does hai să mergem mean, and how is that construction formed?

hai + să + verb-subjunctive is the standard way to say let’s… in Romanian.

hai literally comes from an old imperative of a da but now functions like “come on” or “let’s.”
să introduces the subjunctive (conjunctiv) mood.
mergem is the first-person plural subjunctive of a merge (“to go”).
Together, hai să mergem = let’s go.

How can I tell that mergem here is subjunctive and not the indicative?

The giveaway is the particle să in front of it. After să, Romanian always uses the subjunctive (conjunctiv) form, which for a merge is:
• eu să merg
• tu să mergi
• el/ea să meargă
• noi să mergem
• voi să mergeți
• ei/ele să meargă
So să mergem is the subjunctive “that we go,” used after hai to mean “let us go.”

Why is restaurant written as restaurantul here, and what’s the rule?

Romanian uses enclitic definite articles—meaning you attach the article to the end of the noun. For masculine singular nouns ending in a consonant, the article is -ul.
• restaurant (a restaurant) + -ul = restaurantul (the restaurant)

Why does the adjective ieftin come after the noun in restaurantul ieftin?

Most descriptive adjectives in Romanian follow the noun. So you say restaurantul ieftin (the cheap restaurant), not ieftin restaurantul. There are exceptions (e.g., possessives, ordinals, some stylistic choices), but simple qualifiers like ieftin go after.

Could I say hai să mergem la un restaurant ieftin instead, and how would that change the meaning?

Yes.
• la un restaurant ieftin = “to an inexpensive restaurant” (unspecified).
• la restaurantul ieftin = “to the inexpensive restaurant” (a specific one you have in mind).
Using un (indefinite article) makes the restaurant non-specific, while the enclitic -ul makes it definite.

Why is the preposition la used before restaurantul ieftin, and could I use în instead?

la is the common preposition for going “to” or being “at” a place: la școală, la film, la restaurant.
în
- accusative (e.g., în restaurant) emphasizes being “inside” the building.
  For invitations like hai să mergem la…, Romanian almost always uses la.

Why is there no subject pronoun (like noi) before mergem?

Romanian is a pro-drop language: verb endings carry person and number. mergem has the -em ending, so it already tells you it’s “we.” Adding noi would be redundant unless you want extra emphasis.

Why is there a comma before hai să mergem, and does punctuation follow English rules here?

Yes. In Romanian, as in English, when a subordinate dacă-clause comes first, you separate it from the main clause with a comma:
Dacă ești liber mâine, hai să mergem…
This improves readability and mirrors the English pattern.