Reply from Uncle Agony
Under normal circumstance the guarantee ranks one of the most onerous documents to be signed because without any consideration or benefit received one can become liable debts that he did not incur and the default of which he has no control entirely.
If there is one thing you need to remember to stay out of civil liability that is to “Never, never be a guarantor” However you mentioned that your friend has signed the Guarantee when he doesn’t understand English. If he is totally uneducated and does not understand English he would have a good chance to challenge the validity agreement based on mistake. However if he is a graduate from a Singapore University he might face an uphill task to establish that defence as the local court will find it hard to assume that a local university graduate does not understand a document in English when he signed it.