Um, if your primary use is typing accented letters, why don’t you just set a compose key? The character sequences you need to type are much more intuitive, and you don’t get this type of problem.
In my case, I have scroll lock (the most useless key on the keyboard) set as a compose key. To get “é”, I type scroll lock, then e, then '.
You can set a compose key using setxkbmap, for instance setxkbmap -option compose:sclk
. (If scroll lock isn’t to your liking, there are a number of other modifier keys that can be used instead—list here, starting around line 810.) You can also specify it permanently using X configuration files, although I don’t know the exact method.
My primary icon theme and widget style are 20+ years old and not flat in the least. You can still have that look and feel on a real computer if you want it (but you may have to compromise elsewhere or do some extra work). On phones, all bets are off.
Dunno what your issue with that icon pack is, but I’d bet there’s a good chance it can be solved with a few file renames or symlinks if you care enough to bother.