Decades into the smartphone era, seven billion people communicate with one finger on a virtual QWERTY keyboard. Why not arrange the keys for one-finger typing, with the spacebar and most common letters in the center? Jean Ichbiah did that in 1995 with his FITALY keyboard, and no one noticed.
Here are my arrangements:
On the left is Ichbiah's FITALY, to which I've added digits, symbols, and Esperanto diacritics. If you don't use Esperanto, you can fill those seven slots with whatever you like. A long press on a letter gives the symbol below it; feel free to add symbols under the digits and bottom-row letters.
On the right, I've tried to create something similar for Russian. I calculated, for billions of permutations, how far a finger would need to travel to type the complete text of Anna Karenina. In fact there are 263 decillion (2.63×1035) permutations of 32 letters, so mine might not be ideal, but it looks pretty good.
With digits, I put 1, 2, and 3 nearest to the spacebar because 30% of numerals in documents start with 1 and another 30% with 2 or 3, according to the Newcomb–Benford law.
You can use these layouts for free on your Android device. Go to Google Play and install Multiling O. Hold a finger on the spacebar, drag it to Layouts, choose [ + DIY ], and paste the following text:
{ "title":"62FITALY", "onScreen":{ "main":[ "84zvchwk[DEL]", "62fitaly[ENTER]", "01[SPACE][]ne[SPACE][][SHIFT]", "73gdorsb[SYM:,]", "95qjumpx[ALTGR:.]", "[TOOL] ĵŝĉĝŭĥ[FDEL]" ],"sym":[ " #$_-+= ", " %&<>/* ", " ³²()÷× ", " '\"[]\\@ ", " `^{}|~ ", "" ] } }or
{ "title":"62RUSSIAN", "onScreen":{ "main":[ "84цздмуж[DEL]", "62ылаикч[ENTER]", "01[SPACE][]не[SPACE][][SHIFT]", "73бвотся[SYM:,]", "95хгрпьй[ALTGR:.]", "[TOOL]ъёщшюэф[FDEL]" ],"sym":[ " #$_-+= ", " %&<>/* ", " ³²()÷× ", " '\"[]\\@ ", " `^{}|~ ", "" ] } }To change these layouts, paste them into an editor (I use QuickEdit), then copy and paste the result into Multiling O.