Lua latinic especial chars upper and lower.lua

string.lua

 local upper2lower = {[65]=97,  [66]=98,  [67]=99,  [68]=100, [69]=101, [70]=102, [71]=103, [72]=104,
                      [74]=106, [75]=107, [76]=108, [77]=109, [78]=110, [79]=111, [80]=112, [81]=113,
                      [83]=115, [84]=116, [85]=117, [86]=118, [87]=119, [88]=120, [89]=121, [90]=122,
                      [193]=225,[194]=226,[195]=227,[196]=228,[197]=229,[198]=230,[199]=231,[200]=232,
                      [201]=233,[202]=234,[203]=235,[204]=236,[205]=237,[206]=238,[207]=239,[208]=240,
                      [209]=241,[210]=242,[211]=243,[212]=244,[213]=245,[214]=246,[216]=248,[217]=249,
                      [218]=250,[219]=251,[220]=252,[221]=253,[222]=254,[376]=255,[73]=105, [82]=114,
                      [192]=224};
                      
local lower2upper = {[97]=65,  [98]=66, [99]=67,   [100]=68, [101]=69, [102]=70, [103]=71, [104]=72,[105]=73,
                     [106]=74, [107]=75, [108]=76, [109]=77, [110]=78, [111]=79, [112]=80, [113]=81,[114]=82,
                     [115]=83, [116]=84, [117]=85, [118]=86, [119]=87, [120]=88, [121]=89, [122]=90,[224]=192,
                     [225]=193,[226]=194,[227]=195,[228]=196,[229]=197,[230]=198,[231]=199,[232]=200,
                     [233]=201,[234]=202,[235]=203,[236]=204,[237]=205,[238]=206,[239]=207,[240]=208,
                     [241]=209,[242]=210,[243]=211,[244]=212,[245]=213,[246]=214,[248]=216,[249]=217,
                     [250]=218,[251]=219,[252]=220,[253]=221,[254]=222,[255]=376};
                     
local str_lower = string.lower
local str_upper = string.upper

function string.lower(str,utf8_mode)
  if not utf8_mode then
    return str_lower(str)
  end
  
  local result = ""
  for _,i in utf8.codes(str) do
    result = result..utf8.char(upper2lower[i]==nil and i or upper2lower[i])
  end
  return result
end

function string.upper(str,utf8_mode)
  if not utf8_mode then
    return str_upper(str)
  end
  
  local result = ""
  for _,i in utf8.codes(str) do
    result = result..utf8.char(lower2upper[i]==nil and i or lower2upper[i])
  end
  return result
end

function string.sanitize(str)
  -- find the first invalid byte and return the string up to that point
  local p, len = 1, #str
  while p <= len do
    if str:byte(p) > 127 then
      -- check if the character is a valid multi-byte sequence
      local char_len = 1
      while str:byte(p+char_len-1) > 191 and str:byte(p+char_len-1) < 224 do
        char_len = char_len + 1
      end
      if char_len == 1 then
        -- character is invalid, remove it and move on
        str = str:sub(1, p-1) .. str:sub(p+1)
        len = len - 1
      else
        p = p + char_len - 1
      end
    end
    p = p + 1
  end
  return str
end

I just nicked this for my editor config - https://codeberg.org/lusci/lusci

-- lookups from https://gist.github.com/natanael-b/3de34eff407477cc519eb6a309ebaf14
local utf_lower = { 
 [192]=224, [193]=225, [194]=226, [195]=227, [196]=228, [197]=229, [198]=230, [199]=231, 
 [200]=232, [201]=233, [202]=234, [203]=235, [204]=236, [205]=237, [206]=238, [207]=239, 
 [208]=240, [209]=241, [210]=242, [211]=243, [212]=244, [213]=245, [214]=246, [216]=248, 
 [217]=249, [218]=250, [219]=251, [220]=252, [221]=253, [222]=254, [376]=255 }

local utf_upper = { 
 [224]=192, [225]=193, [226]=194, [227]=195, [228]=196, [229]=197, [230]=198, [231]=199, 
 [232]=200, [233]=201, [234]=202, [235]=203, [236]=204, [237]=205, [238]=206, [239]=207, 
 [240]=208, [241]=209, [242]=210, [243]=211, [244]=212, [245]=213, [246]=214, [248]=216, 
 [249]=217, [250]=218, [251]=219, [252]=220, [253]=221, [254]=222, [255]=376 }
                     
local function utfcaseup(c,lo)
  if lo then c=string.lower(c) lo=utf_lower
  else c=string.upper(c) lo=utf_upper end
  if not c:find("[\194-\244]") then return c end
  
  local r= {}
  for _,i in utf8.codes(c) do  r[#r+1] = utf8.char( lo[i] or i ) end
  return table.concat(r)
end

function upperutf8(c)  return utfcaseup(c)  end
function lowerutf8(c)  return utfcaseup(c,"low") end