Shift–Command–Left/Right Arrow started switching tabs in macOS Mojave Finder, clashes with text movement?
If you set your own shortcut for moving between tabs of a window, the Shift-Command-Arrow combinations will work as before. 

To set your own shortcut: 


Open System Preferences -> Keyboard -> Shortcuts
Select App Shortcuts at the bottom. 
Click the + button to add a shortcut.
Make sure that "All Applications" is selected
Type in the exact names of the commands, on an English system they would be 'Show Previous Tab' and 'Show Next Tab'. Check this in the Window Menu in Finder if you're not sure.
Add your preferred shortcut to switch between tabs in either direction