SSCCE:

module Main exposing (main)

import Browser
import Html
import Html.Events


type Msg
    = Pärtan SubMsg


type SubMsg
    = Ärtan


main =
    Browser.sandbox
        { init =
            { startsWithAscii = Pärtan Ärtan
            , startsWithUnicode = Ärtan
            }
        , update = always identity
        , view =
            \_ ->
                Html.button [ Html.Events.onClick (Pärtan Ärtan) ]
                    [ Html.text "Click me, then open the debugger" ]
        }

Notice how:

• The messages history on the left correctly displays Pärtan Ärtan.
• The current message on the right instead displays Pärtan <internals>.
• The model on the right displays Pärtan <internals> and <internals>.

The reason it works in the messages history but not in the main view is because there are two functions that displays Elm values – and only one of them is correct.

1. _Debugger_messageToString is used for the messages history. In short, it considers custom types with an ASCII lowercase first letter as internal (such as a3, which is a virtual DOM attribute), and all other custom types as displayable. https://github.com/elm/browser/blob/1.0.2/src/Elm/Kernel/Debugger.js#L356-L376

2. _Debugger_init is used for the main view (both for the message and the model). In short, it kind of does the opposite: It considers a custom type with an ASCII uppercase first letter as displayable, and all other custom types as internal. That is equivalent to the approach in _Debugger_messageToString – but only for ASCII. Elm supports custom type variants that starts with any unicode uppercase letter. https://github.com/elm/browser/blob/1.0.2/src/Elm/Kernel/Debugger.js#L439-L451

The solution is to use the _Debugger_messageToString approach in _Debugger_init too: Hide ASCII lowercase, and display others.

Expected: