documentclass{article}
usepackage{fontspec}
usepackage{ifluatex,ifxetex}

setmainfont[Mapping=cyrillic-to-latin]{texgyreadventor-regular.otf}

begin{document}
ifxetex
    This is XeTeX
elseifluatex
    This is LuaTeX
fifi

Hello, world

Здравствуй, Мир

end{document}

; TECkit mapping for TeX input conventions <-> Unicode characters

LHSName "Cyrillic-to-Latin"
RHSName "UNICODE"

pass(Unicode)

; ligatures from Knuth's original CMR fonts
U+002D U+002D           <>  U+2013  ; -- -> en dash
U+002D U+002D U+002D    <>  U+2014  ; --- -> em dash

U+0027          <>  U+2019  ; ' -> right single quote
U+0027 U+0027   <>  U+201D  ; '' -> right double quote
U+0022           >  U+201D  ; " -> right double quote

U+0060          <>  U+2018  ; ` -> left single quote
U+0060 U+0060   <>  U+201C  ; `` -> left double quote

U+0021 U+0060   <>  U+00A1  ; !` -> inverted exclam
U+003F U+0060   <>  U+00BF  ; ?` -> inverted question

; additions supported in T1 encoding
U+002C U+002C   <>  U+201E  ; ,, -> DOUBLE LOW-9 QUOTATION MARK
U+003C U+003C   <>  U+00AB  ; << -> LEFT POINTING GUILLEMET
U+003E U+003E   <>  U+00BB  ; >> -> RIGHT POINTING GUILLEMET


U+0410 <> U+0041  ; A
U+0411 <> U+0042  ; B
U+0412 <> U+0056  ; V
U+0413 <> U+0047  ; G
U+0414 <> U+0044  ; D
U+0415 <> U+0045  ; E
U+0416 <> U+017D  ; Ž
U+0417 <> U+005A  ; Z
U+0418 <> U+0049  ; I
U+041A <> U+004B  ; K
U+041B <> U+004C  ; L
U+041C <> U+004D  ; M
U+041D <> U+004E  ; N
U+041E <> U+004F  ; O
U+041F <> U+0050  ; P
U+0420 <> U+0052  ; R
U+0421 <> U+0053  ; S
U+0422 <> U+0054  ; T
U+0423 <> U+0055  ; U
U+0424 <> U+0046  ; F
U+0426 <> U+0043  ; C
U+0427 <> U+010C  ; Č
U+0428 <> U+0160  ; Š
U+042D <> U+0116  ; Ė
U+042E <> U+004A U+0075  ; Ju
U+042F <> U+004A U+0061  ; Ja
U+0401 <> U+00CB  ; Ë
U+0430 <> U+0061  ; a
U+0431 <> U+0062  ; b
U+0432 <> U+0076  ; v
U+0433 <> U+0067  ; g
U+0434 <> U+0064  ; d
U+0435 <> U+0065  ; e
U+0436 <> U+017E  ; ž
U+0437 <> U+007A  ; z
U+0438 <> U+0069  ; i
U+0439 <> U+006A  ; j
U+043A <> U+006B  ; k
U+043B <> U+006C  ; l
U+043C <> U+006D  ; m
U+043D <> U+006E  ; n
U+043E <> U+006F  ; o
U+043F <> U+0070  ; p
U+0440 <> U+0072  ; r
U+0441 <> U+0073  ; s
U+0442 <> U+0074  ; t
U+0443 <> U+0075  ; u
U+0444 <> U+0066  ; f
U+0446 <> U+0063  ; c
U+0447 <> U+010D  ; č
U+0448 <> U+0161  ; š
U+044D <> U+0117  ; ė
U+044E <> U+006A U+0075  ; ju
U+044F <> U+006A U+0061  ; ja
U+0451 <> U+00EB  ; ë
U+0456 <> U+0069  ; i
U+0406 <> U+0049  ; I
U+0454 <> U+006A U+0065  ; je
U+0468 <> U+004A U+0065  ; Je
U+0425 <> U+0043 U+0068 ; Ch
U+0445 <> U+0063 U+0068 ; ch
U+0418 <> U+0049  ; I
U+0429 <> U+0160  U+010D ; Šč
U+042A <> U+0027  ; '
U+042B <> U+0059  ; Y
U+042C <> U+2019  ; '
U+0449 <> U+0161  U+010D ; šč
U+044A <> U+2019  ; '
U+044B <> U+0079  ; y
U+044C <> U+2019  ; '

maptofea.lua Convert teckit map files to OpenType feature files
Usage:
texlua maptofea.lua [options] <map file> [glyph list file]
-l,--language  (default dflt) language name in OpenType format
-s,--script  (default LATN) script name in OpenType format
<map_file> (string) file to be converted
[glyph_list] (defualt glyphlist.txt) file in Adobe glyh list format with unicode to glyph names mapping

texlua maptofea.lua cyrillic-to-latin.map > cyrtolatn2.fea

languagesystem LATN dflt;
feature liga {
  sub hyphen hyphen by endash;
  sub hyphen hyphen hyphen by emdash;
  sub quotesingle quotesingle by quotedblright;
  sub grave grave by quotedblleft;
  sub exclam grave by exclamdown;
  sub question grave by questiondown;
  sub comma comma by quotedblbase;
  sub less less by guillemotleft;
  sub greater greater by guillemotright;
} liga;
feature ccmp {
  sub afii10048 by J u;
  sub afii10049 by J a;
  sub iucyrillic by j u;
  sub iacyrillic by j a;
  sub ecyrillic by j e;
  sub Yuslittleiotifiedcyrillic by J e;
  sub afii10043 by Scaron Ccaron;
  sub shchacyrillic by scaron ccaron;
} ccmp;
feature gsub {
  sub quotesingle by quoteright;
  sub grave by quoteleft;
  sub afii10017 by A;
  sub afii10018 by B;
  sub afii10019 by V;
  sub afii10020 by G;
  sub afii10021 by D;
  sub afii10022 by E;
  sub afii10024 by Zcaron;
  sub afii10025 by Z;
  sub afii10026 by J;
  sub afii10028 by K;
  sub afii10029 by L;
  sub afii10030 by M;
  sub afii10031 by N;
  sub afii10032 by O;
  sub afii10033 by P;
  sub afii10034 by R;
  sub afii10035 by S;
  sub afii10036 by T;
  sub afii10037 by U;
  sub afii10038 by F;
  sub afii10040 by C;
  sub afii10041 by Ccaron;
  sub afii10042 by Scaron;
  sub afii10047 by Edotaccent;
  sub afii10023 by Edieresis;
  sub afii10065 by a;
  sub becyrillic by b;
  sub vecyrillic by v;
  sub gecyrillic by g;
  sub decyrillic by d;
  sub iecyrillic by e;
  sub zhecyrillic by zcaron;
  sub zecyrillic by z;
  sub iicyrillic by i;
  sub iishortcyrillic by j;
  sub kacyrillic by k;
  sub elcyrillic by l;
  sub emcyrillic by m;
  sub encyrillic by n;
  sub ocyrillic by o;
  sub pecyrillic by p;
  sub ercyrillic by r;
  sub escyrillic by s;
  sub tecyrillic by t;
  sub ucyrillic by u;
  sub efcyrillic by f;
  sub tsecyrillic by c;
  sub checyrillic by ccaron;
  sub shacyrillic by scaron;
  sub ereversedcyrillic by edotaccent;
  sub iocyrillic by edieresis;
  sub icyrillic by i;
  sub afii10055 by I;
  sub afii10039 by X;
  sub khacyrillic by x;
  sub afii10026 by I;
  sub afii10044 by quotesingle;
  sub afii10045 by Y;
  sub afii10046 by quoteright;
  sub hardsigncyrillic by quoteright;
  sub yericyrillic by y;
  sub softsigncyrillic by quoteright;
} gsub;

documentclass{article}
usepackage{fontspec}
usepackage{ifluatex,ifxetex}

setmainfont[Mapping=cyrillic-to-latin,FeatureFile=cyrtolatn2.fea, RawFeature={+gsub;+liga;}]{Linux Libertine O}

begin{document}
ifxetex
    This is XeTeX
elseifluatex
    This is LuaTeX
fifi

Hello,, -- ---  world я щ
Здравствуй, Мир

end{document}

directlua{
    fonts.handlers.otf.addfeature {
        name = "myliga",
         type = "ligature",
         data = {
             ['Aacute'] = { "А", 0x0301},
             ['Eacute'] = { "Е", 0x0301},
             ['Iacute'] = { "И", 0x0301},
             ['iacute'] = { "и", 0x0301},
             ['Oacute'] = { "О", 0x0301},
             ['Uacute'] = { "У", 0x0301},
             ['Yacute'] = { "Ы", 0x0301},
             ['Egrave'] = { "Э", 0x0301},
             ['egrave'] = { "э", 0x0301},
        },
    }
}

directlua{
    fonts.handlers.otf.addfeature {
        name = "mycomp",
         type = "multiple",
         data = {
             afii10039 = { "C", "h" },
             afii10087 = { "c", "h" },
             afii10048 = { "J", "u" },
             afii10049 = { "J", "a" },
             afii10096 = { "j", "u" },
             afii10097 = { "j", "a" },
             Yuslittleiotifiedcyrillic = { "J", "e" },
             afii10043 = { "Scaron", "ccaron" },
             afii10091 = { "scaron", "ccaron" },
        },
    }
}

directlua{
    fonts.handlers.otf.addfeature {
        name = "mysub",
            type = "substitution",
            data = {
                ["quotesingle"] = "quoteright",
                ["grave"] = "quoteleft",
                ["afii10017"] = "A",
                ["afii10018"] = "B",
                ["afii10019"] = "V",
                ["afii10020"] = "G",
                ["afii10021"] = "D",
                ["afii10022"] = "E",
                ["afii10024"] = "Zcaron",
                ["afii10025"] = "Z",
                ["afii10026"] = "I",
                ["afii10027"] = "J",
                ["afii10028"] = "K",
                ["afii10029"] = "L",
                ["afii10030"] = "M",
                ["afii10031"] = "N",
                ["afii10032"] = "O",
                ["afii10033"] = "P",
                ["afii10034"] = "R",
                ["afii10035"] = "S",
                ["afii10036"] = "T",
                ["afii10037"] = "U",
                ["afii10038"] = "F",
                ["afii10040"] = "C",
                ["afii10041"] = "Ccaron",
                ["afii10042"] = "Scaron",
                ["afii10047"] = "Edotaccent",
                ["afii10023"] = "Edieresis",
                ["afii10065"] = "a",
                ["afii10066"] = "b",
                ["afii10067"] = "v",
                ["afii10068"] = "g",
                ["afii10069"] = "d",
                ["afii10070"] = "e",
                ["afii10072"] = "zcaron",
                ["afii10073"] = "z",
                ["afii10074"] = "i",
                ["afii10075"] = "j",
                ["afii10076"] = "k",
                ["afii10077"] = "l",
                ["afii10078"] = "m",
                ["afii10079"] = "n",
                ["afii10080"] = "o",
                ["afii10081"] = "p",
                ["afii10082"] = "r",
                ["afii10083"] = "s",
                ["afii10084"] = "t",
                ["afii10085"] = "u",
                ["afii10086"] = "f",
                ["afii10088"] = "c",
                ["afii10089"] = "ccaron",
                ["afii10090"] = "scaron",
                ["afii10095"] = "edotaccent",
                ["afii10071"] = "edieresis",
                ["afii10103"] = "i",
                ["afii10055"] = "I",
                ["afii10026"] = "I",
                ["afii10044"] = "quoteright",
                ["afii10045"] = "Y",
                ["afii10046"] = "quoteright",
                ["afii10092"] = "quoteright",
                ["afii10093"] = "y",
                ["afii10094"] = "quoteright",
        },
    }
}

setmainfont{Linux Libertine O}[RawFeature={+mysub;+mycomp;+myliga}]

documentclass{article}
usepackage{fontspec}
usepackage{ifluatex,ifxetex}

setmainfont[Mapping=cyrillic-to-latin]{texgyreadventor-regular.otf}

begin{document}
ifxetex
    This is XeTeX
elseifluatex
    This is LuaTeX

directlua{require("cyrtr")}

fi

Hello, world

Здравствуй, Мир

end{document}

function cyrtr (s)
return
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
string.gsub(
s,
'А','A'),
'Б','B'),
'В','V'),
'Г','G'),
'Д','D'),
'Е','E'),
'Ж','Ž'),
'З','Z'),
'И','I'),
'К','K'),
'Л','L'),
'М','M'),
'Н','N'),
'О','O'),
'П','P'),
'Р','R'),
'С','S'),
'Т','T'),
'У','U'),
'Ф','F'),
'Ц','C'),
'Ч','Č'),
'Ш','Š'),
'Э','Ė'),
'Ю','Ju'),
'Я','Ja'),
'Ё','Ë'),
'а','a'),
'б','b'),
'в','v'),
'г','g'),
'д','d'),
'е','e'),
'ж','ž'),
'з','z'),
'и','i'),
'й','j'),
'к','k'),
'л','l'),
'м','m'),
'н','n'),
'о','o'),
'п','p'),
'р','r'),
'с','s'),
'т','t'),
'у','u'),
'ф','f'),
'ц','c'),
'ч','č'),
'ш','š'),
'э','ė'),
'ю','ju'),
'я','ja'),
'ё','ë'),
'і','i'),
'І','I'),
'є','je'),
'Ѩ','Je'),
'Х','X'),
'х','x'),
'И','I'),
'Щ','Šč'),
'Ы','Y'),
'щ','šč'),
'ы','y')
end


luatexbase.add_to_callback(
"process_input_buffer",
cyrtr,
"cyrillic transliteration")