Thanks!
Small issue #1: this one's on Google, they changed their
standards in Android 5 to put navigation drawers on top of their icons (cool animation notwithstanding). Which I suppose makes sense given Material Design's emphasis on hierarchy-through-drop-shadows. Anyway the animation is an Android system one so it isn't really wasting any meaningful amount of resources and you do still get a little bit of it when you're opening / closing the drawer.
Toolbar issues #1-2: I tend to think that for frequently used buttons at the (harder-to-accurately-position-your-finger-on) top of the screen, generous spacing is a good idea; the search box to me seems plenty big enough, even with the optional history button enabled, and I haven't got any especially compelling extra features I'd like to try to squeeze in.
#3-4: Again, I'm not quite sure what we'd do with the extra space - even on a device with a fairly small screen it's hard to come up with a word that extends outside of the box, unless you're pasting in an entire sentence in which case you're probably out of luck even with fewer / more tightly packed buttons.
#5: It only saves a tap if you're going back exactly one search; for going back two it's a wash and for more than two the menu wins out. Do you often find yourself wanting to go back to the search made just before this one? And does that search reliably show up as the first item in the history menu? (can often find yourself with two or three if say you mis-type something and wait a few seconds before you backspace + correct yourself)
The Palm version of Pleco was a very different beast - had the definition and search result list on the same screen by default (
http://pleco.com/manual/dicttut.html), and the back / forward buttons actually took you back through previous definitions, not through previous searches - previous searches on Palm were done via a drop menu, just like our current history menu. It was also a considerably easier interface to manage extra buttons in, since we were dealing with stylus input exclusively and cramming 9 buttons into a toolbar was no big deal.
#6: That fits with your other suggestions (and in fact I like it better than squeezing the existing buttons into tighter spaces), but again I'm not sold on why we need more space.