When I create an index with a key containing accented characters, they disappear in the index for Microsoft HTML Help output (e.g. "First" => "First").
To reproduce :
I have also set the output language and the topic language to French but it doesn't change anything.
Bit of a guess here. Is your operating system also French? I wonder if it's the same underlying problem as described in Item 11 at Snippets (grainge.org)
Beyond that, I don't know the cause.
My site www.grainge.org includes many free Authoring and RoboHelp resources that may be of help.
My system is indeed in French.
I followed the recommendations described on item 11 at Sippets (diagnostics and reinstall Microsoft Help Compiler) but it doesn't work any better
In my previous post you have to read (ex: "Première" => "Premire")
I tried with RH2019 New UI without changing windows settings, project settings or file settings, and "Première" appears in the chm index correctly.
I also tried on a different computer with RH2020 and the accented character is deleted, even when I change all of the settings. So to me it seems to be a problem with RH2020.
See the following page for support contact options. The email address is recommended as it goes to dedicated RH people.
Thank you for your confirmation that is a 2020 version problem.
I have already contacted support but no answer yet