Localization in ASP.NET Core using Resource (.resx) files

Localization in ASP.NET Core works much the same way as it did in legacy ASP.NET

You need only create .resx files with your translations reference them with an instance of IStringLocalizer<YourControllerName> that you can add to your controller method that contains the model that will use and present the translations to the UI.

First, add the below to ConfigureServices() or similiar method in Startup.cs or Program.cs:

       services.Configure<RequestLocalizationOptions>(options =>  
       {  
         options.SetDefaultCulture("en-US");  
         options.AddSupportedCultures("en-US", "es-CO", "fr-CA");  
         options.AddSupportedUICultures("en-US", "es-CO", "fr-CA");  
       });  

Next add resource (.resx) files (in this example for default American English, Spanish (Colombia), and French (Canada))

Your default .resx will look like this (same language for keys and values); make translations for the Values of es-CO and fr-CA

Now, the results - the translations, the latter two after changing browser default language to es-CO and fr-CA

Reference: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/localization?view=aspnetcore-6.0