Learn Polish: To urządzenie jest bardzo stare, więc zaprojektujemy nowe. - This device is very old, so we will design a new one.

Yes, you could say ... stare, zatem zaprojektujemy nowe. Both więc and zatem express a consequence (meaning "so" or "therefore"). Więc is very common in everyday speech, while zatem sounds slightly more formal, similar to "therefore" in English.

Does więc always need a comma before it here?

Yes! In Polish, you must put a comma before words that connect two clauses to show a consequence, like więc, zatem, or dlatego. This is a strict punctuation rule, unlike in English where "so" sometimes doesn't get a comma.

Why is zaprojektujemy translated as "we will design" when it doesn't use the future helper word będziemy?

Zaprojektować is a perfective verb, meaning it focuses on completing an action. When you conjugate a perfective verb with present-tense endings (like the -emy here for "we"), it automatically creates the future tense. You only use będziemy with imperfective verbs.

Where is the word for "one" in "a new one"? Why does the sentence just end with nowe?