If there's even one important situation where it is necessary to disable text selection, then disabling text selection must be supported.

I gave you several examples of these. The text for many UI elements isn't supposed to be selectable, because it interferes with user interaction.

Your off-chance example where somebody is trying to copy-paste the text for translation because the application is in a foreign language is subordinate to this.

Good UX is about choosing the right tradeoffs between functionality and usability.