Authors CurseForge

Your link is broken.

The default UI abbrieviates ctrl, shift, and alt to c, s and a. So I'm not sure what "Maj" is, or what language that is. :)

might just be a localization thing or something in the client

This is a Blizzard bug.

Look at UIParent.lua, in the function GetBindingText():

    local modKeys = ''; 
    if ( not dashIndex ) then 
        dashIndex = 0; 
    else 
        modKeys = strsub(name, 1, dashIndex); 
 
        if ( tempName == "CAPSLOCK" ) then 
            gsub(tempName, "CAPSLOCK", "Caps"); 
        end 
         
        -- replace for all languages 
        -- for the "push-to-talk" binding 
        modKeys = gsub(modKeys, "LSHIFT", LSHIFT_KEY_TEXT); 
        modKeys = gsub(modKeys, "RSHIFT", RSHIFT_KEY_TEXT); 
        modKeys = gsub(modKeys, "LCTRL", LCTRL_KEY_TEXT); 
        modKeys = gsub(modKeys, "RCTRL", RCTRL_KEY_TEXT); 
        modKeys = gsub(modKeys, "LALT", LALT_KEY_TEXT); 
        modKeys = gsub(modKeys, "RALT", RALT_KEY_TEXT); 
         
        -- use the SHIFT code if they decide to localize the CTRL further. The token is CTRL_KEY_TEXT 
        if ( GetLocale() == "deDE") then 
            modKeys = gsub(modKeys, "CTRL", "STRG"); 
        end 
        -- Only doing French for now since all the other languages use SHIFT, remove the "if" if other languages localize it 
        if ( GetLocale() == "frFR" ) then 
            modKeys = gsub(modKeys, "SHIFT", SHIFT_KEY_TEXT); 
        end 
    end 
 
    if ( returnAbbr ) then 
        if ( count > 1 ) then 
            return "·"; 
        else  
            modKeys = gsub(modKeys, "CTRL", "c"); 
            modKeys = gsub(modKeys, "SHIFT", "s"); 
            modKeys = gsub(modKeys, "ALT", "a"); 
            modKeys = gsub(modKeys, "STRG", "st"); 
        end 
    end 

As you can see, for frFR, "SHIFT" is replaced with "MAJ" (SHIFT_KEY_TEXT). Later, if Abbreviations are requested (returnAbbr evaluates to true) the "SHIFT" is replaced with a "s". Obviously, in frFR, there's no "SHIFT" to replace.

Modifying GetBindingText() yourself is a bad idea. Expect tainting of the action bars if you do so.

One solution would be to securely Hook "ActionButton_UpdateHotkeys", which is the function used by Blizzard to update the HotKey text in ActionButtons and that calls GetBindingText. Something like this might be enough:

hooksecurefunc(ActionButton_UpdateHotkeys, function (self)
  local hotkey = _G[self:GetName().."HotKey"]
  hotkey:SetText(hotkey:GetText():replace("MAJ", "m"))
end)

It must be executed once per session. You can make a simple addon, by creating a new Subdirectory in your wow/Interface/AddOns directory, named FixFrenchMaj, for instance.

In this directory, create a file "FixFrenchMaj.TOC" with the following content:

# Interface: 30000
fix.lua

Also create a "fix.lua" file with the following content:

hooksecurefunc(ActionButton_UpdateHotkeys, function (self)
  local hotkey = _G[self:GetName().."HotKey"]
  hotkey:SetText(hotkey:GetText():replace("MAJ", "m"))
end)

Surround ActionButton_UpdateHotkeys with quote marks:
[FONT=monospace]

[/FONT]hooksecurefunc("ActionButton_UpdateHotkeys", function (self) ....

In Perl, we can use \Q and \E to "quote" a string in a pattern so that any special characters are automatically escape. Using "\Q[[test]]+\E" would be the same as "\[\[test\[\]\+". Is there something similar in Lua pattern matching?