A person joining the crew of a UK ship does not seem to understand English very well What action might be taken against the ship and the master if the person is signed on?

If an MCA Superintendent or Proper Officer decides that the person might not understand orders because of insufficient knowledge of English, the ship could be detained under section 51 of the Merchant Shipping Act 1995, and if the ship goes to sea the master could be fined up to Level 5 (£5, 000).