I assume this is translatable text since the widget is often used to do something in the UI that involves showing or changing texts. To give the possibility to make these translatable the whole script is translatable.
You would need to find a widget that does not use 'translatable text' for the script. (I don't know if such exists though).
An alternative would be to put the widget in a snippet in another module which you do not translate at all.
I believe this is because the JavaScript Snippet uses a String internally, so it is showing up as translatable in your Mendix application.
Depending on your use case, an alternative could be to use a JavaScript Action instead that is triggered by a Nanoflow on the page.