This post is intended to help further readers trying to find a solution with accents or special characters not showing up in their text.
First, when you import a font in your project, but sure to edit the font setting by selecting a character preset and processing the font:
See other post in this forum related to this:
For me, everything was working good in the editor and also in the play mode launched from the editor.
My problem was related with special characters not showing when I exported a project and host it on my own server. The problem was related with the config.json file, generated when you export the project.
In config.json, if you have processed the fonts correctly, you should see all letters like this:
In my case, with my automatic workflow to move files by script, my config.json file encoding were modified to ASCII, and thus, broke all the letters in this file.
So, if you can see your specials letters in your project and preview mode, but not when you export it, check the encoding of your config.json file. It should be UTF8.
Hope this will save time for others like me. 