网络上有若干种译法，如：

不忘初心，牢记使命。
Remain true to our original aspiration and keep our mission firmly in mind.
不忘初心，方得始终。
Never forget why you started, and you can accomplish your mission.

不忘初心，牢记使命
staying true to our founding mission

或者The very beginning mind itself is the most accomplished mind of true enlightenment.【乔布斯】

今天在一本书中看到一个词语“the abandonment of initial ambitions”，我觉得将“初心”译为“initial ambitions”也挺不错。