To switch between workspaces on Deepin, use Super (Windows key) + Left/Right Arrow. You can also press Super + S to enter the multitasking view, which gives you a visual overview of all active desktops.

As for your language switching issue, Deepin 25 often defaults to Super + Space for Input Sources, rather than the traditional Alt + Shift. If that doesn't work, you'll need to head to Control Center > Keyboard > Keyboard Layout to manually bind your preferred shortcut, as some default bindings can be "sticky" or unassigned in this specific community build.

Thank you my friend for your reply! However nothing of this shortcuts does work for me regrettably. I had already tried them all before I posted this thread. Perhaps it's a "LightDM" issue. I'm gonna try and check "DDM" on my Deepin build instead.

I was right after all! It's a LighrDM bug most certainly. So the shortcuts for the switching between desktops and input methods DON'T work on LightDM (X11), and DO work on DDM (Treeland).