Add DOTNET_CLI_UI_LANGUAGE=en to Docker containers

This forces .NET CLI/MSBuild to use English output regardless of host
locale settings. The existing LC_ALL setting doesn't affect .NET CLI
which uses its own language configuration.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: gfraiteur

Dockerfile

@@ -17,6 +17,7 @@ ENV RUNNING_IN_DOCKER=TRUE
 # Set locale for consistent behavior regardless of host locale
 ENV LANG=C.UTF-8
 ENV LC_ALL=C.UTF-8
+ENV DOTNET_CLI_UI_LANGUAGE=en
 
 # Add Windows PowerShell to PATH (pwsh added later by PowershellComponent)
 ENV PATH="C:\Windows\System32\WindowsPowerShell\v1.0;${PATH}"

Dockerfile.claude

@@ -17,6 +17,7 @@ ENV RUNNING_IN_DOCKER=TRUE
 # Set locale for consistent behavior regardless of host locale
 ENV LANG=C.UTF-8
 ENV LC_ALL=C.UTF-8
+ENV DOTNET_CLI_UI_LANGUAGE=en
 
 # Add Windows PowerShell to PATH (pwsh added later by PowershellComponent)
 ENV PATH="C:\Windows\System32\WindowsPowerShell\v1.0;${PATH}"

src/PostSharp.Engineering.BuildTools/Docker/PrologComponent.cs

@@ -33,6 +33,7 @@ public override void WriteDockerfile( TextWriter writer )
             # Set locale for consistent behavior regardless of host locale
             ENV LANG=C.UTF-8
             ENV LC_ALL=C.UTF-8
+            ENV DOTNET_CLI_UI_LANGUAGE=en
 
             # Add Windows PowerShell to PATH (pwsh added later by PowershellComponent)
             ENV PATH="C:\Windows\System32\WindowsPowerShell\v1.0;${PATH}"