Time to read up about the 9 justification points. By default you have CM centered so nothing will get affected by -D. There is also no -DJ option without an argument as the man page shows.
However, I am a bit sympathetic to the expectation that a centred (CM) text should be moving if you say -D2c/1c, or instance, and that works fine. It is just -DJ that is tied to your justification point. E.g., this shifts by the specified amount:
gmt text -R-5/5/60/63 -Jx1.41d/1.41d london.txt -D-1.5c/2c -B -png t