No — bilingual translation inside a demand costs nothing extra, and no plan upgrade is needed to switch it on.
Translation is part of the core loop, so it behaves the same on every package. When the other side writes in another language, you read the text in your own; the Original (XX) button right beneath it shows or hides the sender's own wording. The translation and the original always sit together, so you are never stuck with only a machine rendering. The same dual view applies in the Messages tab, in demand details, and in the offer text you receive.
There is no surcharge because of how the business works: MarbleMap earns from subscriptions only. No cut is taken from a sale and nothing is metered by usage, so there is no per-message, per-character or per-translation charge either.
What a package changes is market access, not language. Buyers can start free with 2 active demands, while suppliers need a package (Starter, Growth or Scale) to see the marketplace and submit offers. Whichever package you are on, bilingual reading is open — just like sealed-bid fairness.
Also asked as: Do I pay extra for translation? · Which plan includes automatic translation? · Is translation free? · Is translation limited to the top tier?