Dynamic format arguments

A resource value can be a composite format string, and the arguments can come straight from your view model. Add the entry as usual:

Key	AppStrings.resx (English)	AppStrings.de.resx (German)
PeopleInvited	{0} people invited	{0} Personen eingeladen

In code

Localizer.Current.Get(AppStringsKeys.PeopleInvited, peopleCount);

The resolved text and the arguments go to string.Format in the localizer's current culture, so a number or a date formats the way that culture writes it.

In XAML

Bind the LocalizeArgs.Arg0…Arg8 attached properties on the element that carries the localized property — the same XAML in Avalonia and WPF:

<TextBlock l:LocalizeArgs.Arg0="{Binding PeopleCount}"
           Text="{l:Localize {x:Static res:AppStringsKeys.PeopleInvited}}" />

The rendered text re-formats live whenever a bound argument changes and whenever the language switches: PeopleCount = 5 renders 5 people invited, and switching to German re-renders it in place as 5 Personen eingeladen.

Worth knowing

• Nine slots, Arg0 through Arg8. Arguments above the highest set slot are trimmed; a set slot with unset slots below it — say, only Arg2 — formats the gaps as null, which renders empty.
• Arguments are per element. Two localized properties on the same element, for example a localized Text and a localized ToolTip, share the one argument set. Give each its own element when they need different arguments.
• Per-argument format specifiers belong in the resource string — {0:N0} people invited — where a translator can adjust them per language.
• No arguments set, no formatting. An element without any ArgN resolves without composite formatting at all, so a resource value containing a literal { or } keeps working without {{ escaping. The missing-key sentinel is likewise never formatted.
• Keep it simple. For a very complex string, compose the text in the view model with Get(key, args…) rather than wiring many argument slots.
• Composite formatting does not pluralize. 1 people invited is on the resource author; use separate singular and plural resources where it matters.