One option is to obtain the position of the plot with the long legend, and then re-size the other to the same width. But it's pretty ugly though.
Try the following:
clear
clc
data1=[1 2 3 4 5];
data2=[5 4 3 2 1];
figure(1)
subplot(2,1,1)
p1=bar(data1);
ht = legend('Data from measurements and some space so its wide enough','Location','Eastoutside')
hp = gca;
posn1 = hp.Position;
subplot(2,1,2)
p2=bar(data2);
legend('Just text','Location','EastOutside')
hp2 = gca;
posn2 = hp2.Position;
set(hp2,'Position',[posn2(1:2), posn1(3:4)])
You could of course put the legend on the top or bottom with northoutside.
Or have a mult-line legend
ht = legend(['Data from measurements', newline 'and some space so its' newline 'wide enough'],'Location','Eastoutside')
