gettext is using the elixir AST to determine if the supplied msgid is just a string or something more involved. In your case the AST for "Displaying" <> " " is no longer just a string, but something which does result in a string when being executed. The execution of it would only happen at runtime so the compiler does not yet know the resulting string to work with and therefore returns an error. One could say that the compiler should optimize away the concat operator in such cases, but it seems that’s just not the case right now.

Use the functions in the Gettext module instead of the macros of MyApp.Gettext.

Thank you for the help @LostKobrakai

Can I ask you what are domain-based translations? I don’t understand:

# Simple translation
gettext("Here is one string to translate")

# Plural translation
number_of_apples = 4
ngettext("The apple is ripe", "The apples are ripe", number_of_apples)

# Domain-based translation
dgettext("errors", "Here is an error message to translate")

What is “errors” for in the last example?