Please help us help you and fill where relevant:
Your LimeSurvey version: [see right hand bottom of your LimeSurvey admin screen]
Own server or LimeSurvey hosting:
Survey theme/template:
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On the data protection page, if a user clicks “continue” but does not agree to the terms, they are shown a popup that in English that reads “Please tick this box if you want to proceed”. If possible, I would like to edit this text and translate to a different language, however after looking through the CSS / JS in the templets theme I was unable to find where this text is being generated. 

The survey is currently deployed on LimeSurvey Version 3.28.54 hosted on a local server. I believe this translation is fixed in the most recent version of LimeSurvey cloud, however for the moment being updating the version is not an option. 

Hi,
this is not LimeSurvey related.
This is the behaviour of the browser.
Try some browsers (Chrome, Firefox, Edge,...) and you will see different boxes and different texts.

Firefox
 
Chrome
 
Edge
 

This is German text, but here you also see the differences
Joffm

Can be updated in javascript

But don't think it's a good idea.

stackoverflow.com/questions/13798313/set...d-validation-message