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which occurs at runtime. Expressions in an interpolated string must reference names in the current
context and need to be stored in resource files. That means that if you want to use localization you
have to do it like:

var FirstName = "John";

// method using different resource file "strings"
// for French ("strings.fr.resx"), German ("strings.de.resx"),
// and English ("strings.en.resx")
void ShowMyNameLocalized(string name, string middlename = "", string surname = "")
{
// get localized string
var localizedMyNameIs = Properties.strings.Hello;
// insert spaces where necessary
name = (string.IsNullOrWhiteSpace(name) ? "" : name + " ");
middlename = (string.IsNullOrWhiteSpace(middlename) ? "" : middlename + " ");
surname = (string.IsNullOrWhiteSpace(surname) ? "" : surname + " ");
// display it
Console.WriteLine($"{localizedMyNameIs} {name}{middlename}{surname}".Trim());
}

// switch to French and greet John
Thread.CurrentThread.CurrentUICulture = CultureInfo.GetCultureInfo("fr-FR");
ShowMyNameLocalized(FirstName);

// switch to German and greet John
Thread.CurrentThread.CurrentUICulture = CultureInfo.GetCultureInfo("de-DE");
ShowMyNameLocalized(FirstName);

// switch to US English and greet John
Thread.CurrentThread.CurrentUICulture = CultureInfo.GetCultureInfo("en-US");
ShowMyNameLocalized(FirstName);

If the resource strings for the languages used above are correctly stored in the individual resource
files, you should get the following output:

Bonjour, mon nom est John
Hallo, mein Name ist John
Hello, my name is John

Note that this implies that the name follows the localized string in every language. If that is not the
case, you need to add placeholders to the resource strings and modify the function above or you
need to query the culture info in the function and provide a switch case statement containing the
different cases. For more details about resource files, see How to use localization in C#.

It is a good practice to use a default fallback language most people will understand, in case a
translation is not available. I suggest to use English as default fallback language.

Recursive interpolation

Although not very useful, it is allowed to use an interpolated string recursively inside another's
curly brackets:

https://riptutorial.com/ 144