I do not recomand the windows notepad for French people and I think it could be the same for German.
By default, the windows notepad use ANSI character encoding instead of UTF-8.
If you save the addon lua files with ANSI encoding, you have to replace special character in string, for example :
é is replaced by \195\169
è is replaced by \195\168
etc
And NEVER open any files in WTF folder with the windows notepad. It will convert the file under ANSI character and the game WOW is unable to read the file. All your addons will be reseted.
So use other editors, but always use UTF-8 as default character encoding.
BTW, my favorite editor is JEdit