Is there a way to remap keys in foreign layout by modifying existing layout or creating your own?
Yosemite (as well as Mavericks before that) has "Russian-PC" and "Russian" layout, both missing "ё" letter. PC layout normally would map it to '`' key, to the left from 1.
Best Answer
Here is a custom Russian PC layout you can download which has the ë where you expect it, even though you are using an ANSI keyboard instead of an ISO one.
https://dl.dropboxusercontent.com/u/46870715/k/RussianPC2.keylayout