Is the failure to report another source of income, or to report its true nature—such as by declaring a low value for the income in a European country—considered a form of deception that makes the money unlawful (haram)?

Muslims in Western countries should be role models in truthfulness and fulfilling conditions, based on the hadith: "Muslims are bound by their conditions." Therefore, if aid for the unemployed is conditional, these conditions must be adhered to, and it is not permissible to circumvent them. As for taxes and tax evasion, please refer to Fatwa No. 11198.