Language Pack Not Found in .NET MAUI Android
Loading a non-English language (for example Chinese) in a .NET MAUI Android project can fail at runtime, even when the trained data sits in Assets/tessdata and is marked as an AndroidAsset.
System.IO.FileNotFoundException: Language Pack Not Found: chi_sim.traineddataBuilding a MAUI Android project from Visual Studio Code or the CLI can skip resolving the language data files IronOCR needs. The *.traineddata files never make it into the APK, so the engine cannot find them at runtime.
Solution
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.csproj3. 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>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();
}
}
}Debug Tips
- Confirm the NuGet package: make sure
IronOcr.Androidis installed and restored. - Turn on logging to see the search paths IronOCR uses for language files:
IronOcr.Installation.LoggingMode = IronOcr.Installation.LoggingModes.All;
IronOcr.Installation.LogFilePath = "OcrMaui.log";
Curtis Chau holds a Bachelor’s degree in Computer Science (Carleton University) and specializes in front-end development with expertise in Node.js, TypeScript, JavaScript, and React. Passionate about crafting intuitive and aesthetically pleasing user interfaces, Curtis enjoys working with modern frameworks and creating well-structured, visually appealing manuals.
