For example Is it possible to understand what the currency of an account is from the account number. Is there a global standard for this or all banks have their own ?
All banks have their own standards. Some Bank use different series of numbers for different currencies. Some Banks use different series to determine local vs non local currencies.
The practise also varies from country to country
If you're using an IBAN then the first two characters mark the country of origin, which will also indicate the currency (but not with certainty, since once can have foreign-currency accounts). The rest is typically based on old national standards, and there every country has its own, and in many each bank also has its own rules.