diff --git a/tests/merge.rs b/tests/merge.rs
index 2445833..d61c280 100644
--- a/tests/merge.rs
+++ b/tests/merge.rs
@@ -7161,6 +7161,7 @@ fn merge_subcommand_git_merge_flags() {
 /// Test repository state validation in the merge command
 #[test]
 fn merge_subcommand_repository_state_validation() {
+    std::env::set_var("LANG", "C");
     println!("\n=== TEST: MERGE SUBCOMMAND REPOSITORY STATE VALIDATION ===");
     let repo_name = "merge_repo_state_validation";
     let repo = setup_git_repo(repo_name);
@@ -7325,7 +7326,7 @@ fn merge_subcommand_repository_state_validation() {
             );
 
             assert!(
-                stdout.contains("Chain feature_chain"),
+                stdout.contains("Chain: feature_chain"),
                 "Output should mention the chain name, got: {}",
                 stdout
             );
diff --git a/tests/merge_base_failures.rs b/tests/merge_base_failures.rs
index e43c624..14c0f76 100644
--- a/tests/merge_base_failures.rs
+++ b/tests/merge_base_failures.rs
@@ -12,6 +12,7 @@ use git2::RepositoryState;
 /// that can confuse fork-point detection.
 #[test]
 fn test_complex_rebased_remote_history() {
+    std::env::set_var("LANG", "C");
     let repo_name = "complex_rebased_remote";
     let repo = setup_git_repo(repo_name);
     let path_to_repo = generate_path_to_repo(repo_name);
diff --git a/tests/rebase.rs b/tests/rebase.rs
index abe2a72..67d7644 100644
--- a/tests/rebase.rs
+++ b/tests/rebase.rs
@@ -1077,6 +1077,7 @@ chain_name
 
 #[test]
 fn rebase_no_forkpoint() {
+    std::env::set_var("LANG", "C");
     let repo_name = "rebase_no_forkpoint";
     let repo = setup_git_repo(repo_name);
     let path_to_repo = generate_path_to_repo(repo_name);