Language Pack Not Found in .NET MAUI Android

1. Build in Visual Studio 2022

Open and build the project in the full Visual Studio 2022 IDE (v17.10 or later). The full IDE includes the dependencies in the Android APK during the build, which the CLI and VS Code paths can miss.

2. Relocate the OcrData folder

After the build, move the OcrData folder out of bin and into the project root, for example OcrData/chi_sim.traineddata.

ProjectRoot/
├── OcrData/
│   └── chi_sim.traineddata
├── Resources/
│   └── Fonts/
│       └── NotoSansSC-Regular.ttf
├── MyMauiApp.csproj

3. Register the trained data as Android assets

Add the relocated files to your .csproj so they ship with the APK:

<ItemGroup>
  <AndroidAsset Include="OcrData\chi_sim.traineddata" />
  <AndroidAsset Include="ocrData\chi_tra.traineddata" />
</ItemGroup>

<ItemGroup>
  <AndroidAsset Include="OcrData\chi_sim.traineddata" />
  <AndroidAsset Include="ocrData\chi_tra.traineddata" />
</ItemGroup>

4. Add a font that supports your characters

Recognized text still needs a font that can render it in the app UI. Drop a font such as Noto Sans SC into Resources/Fonts and register it in MauiProgram.cs:

using Microsoft.Extensions.Logging;
namespace MauiApp2
{
    public static class MauiProgram
    {
        public static MauiApp CreateMauiApp()
        {
            var builder = MauiApp.CreateBuilder();
            builder
                .UseMauiApp<App>()
                .ConfigureFonts(fonts =>
                {
                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                    fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
                });
#if DEBUG
            builder.Logging.AddDebug();
#endif
            return builder.Build();
        }
    }
}

using Microsoft.Extensions.Logging;
namespace MauiApp2
{
    public static class MauiProgram
    {
        public static MauiApp CreateMauiApp()
        {
            var builder = MauiApp.CreateBuilder();
            builder
                .UseMauiApp<App>()
                .ConfigureFonts(fonts =>
                {
                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                    fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
                });
#if DEBUG
            builder.Logging.AddDebug();
#endif
            return builder.Build();
        }
    }
}

Imports Microsoft.Extensions.Logging

Namespace MauiApp2

    Public Module MauiProgram

        Public Function CreateMauiApp() As MauiApp
            Dim builder = MauiApp.CreateBuilder()
            builder _
                .UseMauiApp(Of App)() _
                .ConfigureFonts(Sub(fonts)
                                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular")
                                    fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold")
                                End Sub)
#If DEBUG Then
            builder.Logging.AddDebug()
#End If
            Return builder.Build()
        End Function

    End Module

End Namespace