Is there a keyboard shortcut (or a Greasemonkey script that adds this keyboard shortcut), to make a certain paragraph right-to-left, or left-to-right in gmail?
This question in the official gmail forums has no answer.
RCtrl+RShift (as in, the shift and control keys on the right side of the keyboard). Works for me in Chrome and all other Windows apps. In Firefox it's Ctrl+Alt+X.
This is for RTL typing, not for right justified text (similar but different).
This the most complete, pedantic answer possible:
To have some paragraphs LTR and some RTL, you need to have rich formatting enabled. If you don't have rich formatting enabled, the change is temporary and will not be seen on the receiving end of the email. There is no way to send RTL text without enabling rich-formatting because plain text emails don't support the RTL HTML tags.
Clicking the "Right to Left" button on the rich-formatting toolbar has the same effect as typing RCtrl+RShift while rich-formatting is enabled. Typing RCtrl+RShift without rich formatting has only a local effect, unseen at the receiver, and applies to the entire text, not just the current paragraph.