I would be careful with this. Most of the shortcuts mentioned here are already very standard browser and text-editing shortcuts, and users generally expect them to behave in the usual way.
Overriding things like Ctrl/Cmd+A or Ctrl/Cmd+S with app-specific behavior can easily become surprising rather than helpful, especially in a web application. In many cases, consistency with established platform behavior is more valuable than adding custom actions.
The same applies to triple-clicking: that is normal selection behavior, not something unusual that needs special handling. If anything, Kagi Translate should probably preserve expected browser/text-field conventions instead of redefining them.
If custom shortcuts are added, they would be better as additional, clearly documented shortcuts rather than replacements for common defaults.
