“郑重声言”常见的英文表达是 “solemnly declare” 或 “state solemnly”。
solemnly declare 强调以严肃、庄重的方式作出声明，语气较为正式、郑重，常用于正式场合或官方声明中。例如：We solemnly declare that we will adhere to the principles of fairness and justice.（我们郑重声明，我们将坚守公平和正义的原则。）
state solemnly 同样传达出严肃、庄重宣告的意味， “state”有“陈述、声明”之意，“solemnly”修饰，突出郑重态度。例如：The government stated solemnly that it would take all necessary measures to protect the environment.（政府郑重声明，将采取一切必要措施保护环境。 ）