diff --git a/GricheldeChat.lua b/GricheldeChat.lua
index cb6015c..f9bfa8f 100644
--- a/GricheldeChat.lua
+++ b/GricheldeChat.lua
@@ -206,6 +206,15 @@ function Grichelde:ReplaceCharacters(text, replName, replTable, consolidate, rep
                     p, patRest = getNextCharUtf8(patRest)
                 end
                 ciPattern = ciPattern .. "]"
+            elseif (isUtf8MultiByte(p)) then
+                -- a set like [Ää] would match single bytes, so only group the differing last byte
+                local upperP, lowerP = toUpper(p), toLower(p)
+                local lead = sub(p, 1, -2)
+                if (upperP ~= lowerP) and (sub(upperP, 1, -2) == lead) and (sub(lowerP, 1, -2) == lead) then
+                    ciPattern = ciPattern .. lead .. "[" .. sub(upperP, -1) .. sub(lowerP, -1) .. "]"
+                else
+                    ciPattern = ciPattern .. p
+                end
             else
                 ciPattern = ciPattern .. "[" .. convertToCaseInsensitivePatternGroup(p) .. "]"
             end
@@ -428,8 +437,9 @@ function Grichelde:ReplaceCharacters(text, replName, replTable, consolidate, rep
             end
 
             -- update previous consolidate markers
-            local diff = lengthUtf8(replText) - lengthUtf8(match)
-            self:TracePrint("ReplaceCharacters : diff = %d - %d", lengthUtf8(replText), lengthUtf8(match))
+            -- positions are byte offsets, so the difference must be counted in bytes as well
+            local diff = length(replText) - length(match)
+            self:TracePrint("ReplaceCharacters : diff = %d - %d", length(replText), length(match))
             for key, posList in pairs(consolidate) do
                 if (key ~= replName) then
                     for i, pc in ipairs(posList) do
diff --git a/GricheldeConstants.lua b/GricheldeConstants.lua
index 99c2006..a127062 100644
--- a/GricheldeConstants.lua
+++ b/GricheldeConstants.lua
@@ -378,6 +378,24 @@ local function getUtf8Table(word)
     return tbl
 end
 
+--- handles UTF-8 characters like äöü (except ß, ÿ, × and ÷)
+local function toUpper(word)
+    return (Grichelde.F.gsub(_G.strupper(word), "\195([\160-\190])", function(c)
+        if (c ~= "\183") then
+            return "\195" .. Grichelde.F.bytes2Char(Grichelde.F.toByte(c) - 32)
+        end
+    end))
+end
+
+--- handles UTF-8 characters like äöü (except ß, ÿ, × and ÷)
+local function toLower(word)
+    return (Grichelde.F.gsub(_G.strlower(word), "\195([\128-\158])", function(c)
+        if (c ~= "\151") then
+            return "\195" .. Grichelde.F.bytes2Char(Grichelde.F.toByte(c) + 32)
+        end
+    end))
+end
+
 local function isLetter(word)
     local char = Grichelde.F.getNextCharUtf8(word)
     return (char ~= nil) and (Grichelde.F.toUpper(char) ~= Grichelde.F.toLower(char))
@@ -514,8 +532,8 @@ Grichelde.F = {
     gmatch          = _G.string.gmatch,
     join            = _G.strjoin,
     split           = _G.strsplit,
-    toUpper         = _G.strupper,
-    toLower         = _G.strlower,
+    toUpper         = toUpper,
+    toLower         = toLower,
     getNextCharUtf8 = getNextCharUtf8,
     isUtf8MultiByte = isUtf8MultiByte,
     getUtf8Sequence = getUtf8Sequence,
diff --git a/GricheldeTest.lua b/GricheldeTest.lua
index c52aa8c..891f615 100644
--- a/GricheldeTest.lua
+++ b/GricheldeTest.lua
@@ -72,7 +72,7 @@ function Grichelde:RunTests()
             ["OSSO"] = "OCHO",
             ["ooSS"] = "ooCH",
             ["schmeissen"] = "chmeichen",
-            ["Schön"] = "Chön",
+            ["Schön"] = "Chön",
         }
     )
     ok = ok + o
@@ -819,8 +819,9 @@ function Grichelde:RunTests()
         {
             ["Hallä"] = "Hallae",
             ["Ätsch"] = "Aetsch",
-            ["Hällöluü"] = "Haelloelue",
-            ["ÜöÄ"] = "UeoeAe",
+            ["Hällöluü"] = "Haelloeluue",
+            ["ÜöÄ"] = "UeoeAE",
+            ["Ää"] = "Aeae",
         }
     )
     ok = ok + o