“心里”常见的英文表达有 “in one's heart” 或 “in one's mind”，具体使用哪个取决于语境和想要强调的侧重点：
in one's heart：更侧重于情感、内心深处的感受或想法，带有一定的情感色彩。例如：
She knew in her heart that he was telling the truth.（她内心深处知道他在说真话。）
He still loves her in his heart.（他心里依然爱着她。）
in one's mind：更强调思维、想法或观念，侧重于理性的思考和认知。例如：
I have a plan in my mind.（我心里有个计划。）
The image of that scene stayed in my mind for a long time.（那个场景的画面在我脑海里停留了很久。 ）