Learn Romanian: Avem mulți prieteni.

In Romanian, you don't always need to say the subject pronoun like noi (we) because the verb form already tells you who is doing the action. Avem means exactly "we have", so adding noi is optional and usually left out unless you want to emphasize it.

Why is it mulți and not just mult?

Mult means "much" or "a lot", but it changes to match the word it describes. Because prieteni (friends) is masculine and plural, you must use the masculine plural form, which is mulți (many). If you were talking about feminine plural nouns, you would use multe.

How do you say "friend" in the singular?

The singular form is prieten (a male friend). To make most masculine nouns plural in Romanian, you add an -i to the end, making it prieteni.

Do I pronounce the -i at the end of mulți and prieteni like a normal "ee" sound?

No, it is not a full vowel sound. In Romanian, an -i at the end of a word is usually a "whispered i" (unless it is stressed). It doesn't add a new syllable. Instead, it just softens the consonant before it. For mulți, you make a soft "ts" sound, and for prieteni, a soft "n" sound.