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icu-dotnet is the C# wrapper for a subset of ICU4C "ICU for C".

ICU is a mature, widely used set of C/C++ and Java libraries providing Unicode and Globalization support for software applications. ICU is widely portable and gives applications the same results on all platforms and between C/C++ and Java software.


OS Status
Linux Build Status
Windows Build Status


This library provides .NET classes and methods for (a subset of) the ICU C API. Please refer to the ICU API documentation. In icu.net you'll find classes that correspond to the C++ classes of ICU4C.

Although not strictly required it is recommended to call Icu.Wrapper.Init() at the start of the application. This will allow to use icu.net from multiple threads (c.f. ICU Initialization and Termination). Similarly, it might be beneficial to call Icu.Wrapper.Cleanup() before exiting.

Sample code:

	static class Program
		public static void Main(string[] args)
			// Will output "NFC form of XA\u0308bc is XÄbc"
			Console.WriteLine($"NFC form of XA\\u0308bc is {Icu.Normalizer.Normalize("XA\u0308bc",


icu-dotnet can be built with Visual Studio or MonoDevelop, but at least initially it might be easier to build from the command line because that will download all necessary dependencies.


You can build and run the unit tests by running:


If you run into issues you might want to try with a newer mono version or with our custom mono-sil package from packages.sil.org


Build and run the unit tests by running:

msbuild /t:Test build/icu-dotnet.proj

ICU versions


icu-dotnet links with any installed version of ICU shared objects. It is recommended to install the version provided by the distribution. As of 2016, Ubuntu Trusty uses version ICU 52 and Ubuntu Xenial 55.


Rather than using the full version of ICU (which can be ~25 MB), a custom minimum build can be used. It can be installed by the Icu4c.Win.Min nuget package. The full version of ICU is also available as Icu4c.Win.Full.Lib and Icu4c.Win.Full.Bin.

What's in the minimum build

  • Characters
  • ErrorCodes
  • Locale
  • Normalizer
  • Rules-based Collator
  • Unicode set to pattern conversions


  • make sure you added the nuget packages icu.net and Icu4c.Win.Min (or Icu4c.Win.Full).
  • the binaries of the nuget packages need to be copied to your output directory. For icu.net this happens by the assembly reference that the package adds to your project. The binaries of Icu4c.Win.Min are only relevant on Windows. They will get copied by the Icu4c.Win.Min.targets file included in the nuget package.

The package installer should have added an import to the *.csproj file similar to the following:

<Import Project="..\..\packages\Icu4c.Win.Min.54.1.31\build\Icu4c.Win.Min.targets"
	Condition="Exists('..\..\packages\Icu4c.Win.Min.54.1.31\build\Icu4c.Win.Min.targets')" />


We love contributions! The library mainly contains the functionality we need for our products. If you miss something that is part of ICU4C but not yet wrapped in icu.net, add it and create a pull request.

If you find a bug - create an issue on GitHub, then preferably fix it and create a pull request!