A multi-currency wallet is an account structure that holds balances in several currencies at once instead of converting everything into a single base currency. Deposits stay in the currency they arrived in, positions can be settled in the currency they are quoted in, and conversion happens only when the trader chooses it.
The point of the structure is conversion cost. An account with one base currency converts every deposit that arrives in another currency, and converts the profit or loss on every position quoted outside it — a margin on the exchange rate, applied repeatedly, to money that never needed to move. A wallet arrangement removes those forced conversions at the price of more bookkeeping: several balances to watch, margin that may be drawn from one of them in particular, and a total that only means anything once you pick a reporting currency.
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Guide
How to Check the Way a Currency Is Managed
The regime behind a currency is published, not inferred. The four primary sources that say how a rate is governed, what each one can and cannot tell you, and how to keep the answer from going stale.