diff --git a/src/ClaudeDo.Data/Git/GitService.cs b/src/ClaudeDo.Data/Git/GitService.cs
index b2c00879..613724d4 100644
--- a/src/ClaudeDo.Data/Git/GitService.cs
+++ b/src/ClaudeDo.Data/Git/GitService.cs
@@ -704,6 +704,11 @@ public sealed class GitService
             // (mktree "input format error") and would prepend to stdin commit messages.
             StandardInputEncoding = stdinData is not null ? new UTF8Encoding(false) : null,
         };
+        // Force English stderr/stdout so the English-only substring matches below
+        // (e.g. "ambiguous argument 'HEAD'", "tell me who you are") work regardless
+        // of the OS locale git for Windows picks up.
+        psi.Environment["LC_ALL"] = "C";
+        psi.Environment["LANGUAGE"] = "C";
         psi.ArgumentList.Add("-C");
         psi.ArgumentList.Add(workDir);
         foreach (var a in args) psi.ArgumentList.Add(a);
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/GitServiceBootstrapTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/GitServiceBootstrapTests.cs
index 14924db9..4192da5e 100644
--- a/tests/ClaudeDo.Worker.Tests/Runner/GitServiceBootstrapTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Runner/GitServiceBootstrapTests.cs
@@ -122,6 +122,61 @@ public class GitServiceBootstrapTests : IDisposable
         Assert.Equal("ClaudeDo <claudedo@local>", author);
     }
 
+    [Fact]
+    public async Task RevParseHead_EmptyRepo_FriendlyMessage_EvenUnderNonEnglishLocale()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var dir = InitEmptyRepo();
+        var previousLanguage = Environment.GetEnvironmentVariable("LANGUAGE");
+        var previousLcAll = Environment.GetEnvironmentVariable("LC_ALL");
+        // Simulate a non-English OS/git locale on the *ambient* process environment.
+        // GitService must override it per-call so its English-only stderr matches
+        // (e.g. "ambiguous argument 'HEAD'") keep working regardless.
+        Environment.SetEnvironmentVariable("LANGUAGE", "de");
+        Environment.SetEnvironmentVariable("LC_ALL", "de_DE.UTF-8");
+        try
+        {
+            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => _git.RevParseHeadAsync(dir));
+            Assert.Contains("no commits yet", ex.Message);
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("LANGUAGE", previousLanguage);
+            Environment.SetEnvironmentVariable("LC_ALL", previousLcAll);
+        }
+    }
+
+    [Fact]
+    public async Task CommitAsync_MissingIdentity_FallsBackToClaudeDoIdentity_EvenUnderNonEnglishLocale()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var dir = InitEmptyRepo();
+        GitRepoFixture.RunGit(dir, "-c", "user.name=t", "-c", "user.email=t@t", "commit", "--allow-empty", "-m", "seed");
+        GitRepoFixture.RunGit(dir, "config", "user.name", "");
+        GitRepoFixture.RunGit(dir, "config", "user.email", "");
+        File.WriteAllText(Path.Combine(dir, "work.txt"), "content\n");
+        await _git.AddAllAsync(dir);
+
+        var previousLanguage = Environment.GetEnvironmentVariable("LANGUAGE");
+        var previousLcAll = Environment.GetEnvironmentVariable("LC_ALL");
+        Environment.SetEnvironmentVariable("LANGUAGE", "de");
+        Environment.SetEnvironmentVariable("LC_ALL", "de_DE.UTF-8");
+        try
+        {
+            await _git.CommitAsync(dir, "feat(test): identity fallback under non-English locale");
+
+            var author = GitRepoFixture.RunGit(dir, "log", "-1", "--format=%an <%ae>").Trim();
+            Assert.Equal("ClaudeDo <claudedo@local>", author);
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("LANGUAGE", previousLanguage);
+            Environment.SetEnvironmentVariable("LC_ALL", previousLcAll);
+        }
+    }
+
     public void Dispose()
     {
         foreach (var dir in _tempDirs)