This is not related to Plus! but is actually a Windows behavior. Here are the shortcuts you asked for:
- Ctrl+Left Shift - Left alignment (left-to-right text)
- Ctrl+Right Shift - Right alignment (right-to-left text)
However, Messenger will not (for some odd reason) accept these shortcuts until you enter certain special characters into the input box. For example, one character that works is Alt+1986. Once you've entered this character, you can delete it and then use those shortcuts (I don't know why this is required
)