If a language you want to support is not considered canonical, and hence does not include full localization data by default in Blazor, you can use the _ReplaceICU target defined in the .csproj to replace the built-in icudt.dat file with your own.
Refer to this comment to find out how to generate your own file: dotnet/runtime#53239 (comment).
The icudt.dat file included in this project contains the lb-LU culture.