"慢慢写"的英文表达是 "write slowly"。这个表达的来源是由动词 "write" 和副词 "slowly" 组合而成，"write" 意思是写字，"slowly" 意思是慢慢地。

下面是一些例句：

Please write slowly so that I can understand what you are saying. (请慢慢写，这样我就能理解你在说什么。)
She wrote slowly and carefully, making sure not to make any mistakes. (她慢慢地写，小心翼翼，确保不出错。)
He always writes slowly because he wants to make sure that everything is perfect. (他总是慢慢写，因为他想确保一切都完美。)