diff --git a/src/repository/api/ArcanistGitAPI.php b/src/repository/api/ArcanistGitAPI.php
--- a/src/repository/api/ArcanistGitAPI.php
+++ b/src/repository/api/ArcanistGitAPI.php
@@ -21,36 +21,21 @@
     return new ArcanistGitAPI($root);
   }
 
-  protected function buildLocalFuture(array $argv) {
-    $argv[0] = 'git '.$argv[0];
-
-    $future = newv('ExecFuture', $argv);
-    $future->setCWD($this->getPath());
-    return $future;
-  }
-
-  public function execPassthru($pattern /* , ... */) {
-    $args = func_get_args();
-
-    static $git = null;
-    if ($git === null) {
-      if (phutil_is_windows()) {
-        // NOTE: On Windows, phutil_passthru() uses 'bypass_shell' because
-        // everything goes to hell if we don't. We must provide an absolute
-        // path to Git for this to work properly.
+  protected function getBinaryName() {
+    if (phutil_is_windows()) {
+      // NOTE: On Windows, passthru uses 'bypass_shell' because everything
+      // goes to hell if we don't. We must provide an absolute path to Git for
+      // this to work properly.
+      static $git;
+      if ($git === null) {
         $git = Filesystem::resolveBinary('git');
-        $git = csprintf('%s', $git);
-      } else {
-        $git = 'git';
       }
+      return $git;
+    } else {
+      return 'git';
     }
-
-    $args[0] = $git.' '.$args[0];
-
-    return call_user_func_array('phutil_passthru', $args);
   }
 
-
   public function getSourceControlSystemName() {
     return 'git';
   }
diff --git a/src/repository/api/ArcanistMercurialAPI.php b/src/repository/api/ArcanistMercurialAPI.php
--- a/src/repository/api/ArcanistMercurialAPI.php
+++ b/src/repository/api/ArcanistMercurialAPI.php
@@ -12,7 +12,11 @@
   private $supportsRebase;
   private $supportsPhases;
 
-  protected function buildLocalFuture(array $argv) {
+  protected function getBinaryName() {
+    return 'hg';
+  }
+
+  protected function getExecutionEnvironment() {
     // Mercurial has a "defaults" feature which basically breaks automation by
     // allowing the user to add random flags to any command. This feature is
     // "deprecated" and "a bad idea" that you should "forget ... existed"
@@ -23,26 +27,9 @@
     // There is an HGPLAIN environmental variable which enables "plain mode"
     // and hopefully disables this stuff.
 
-    if (phutil_is_windows()) {
-      $argv[0] = 'set HGPLAIN=1 & hg '.$argv[0];
-    } else {
-      $argv[0] = 'HGPLAIN=1 hg '.$argv[0];
-    }
-
-    $future = newv('ExecFuture', $argv);
-    $future->setCWD($this->getPath());
-    return $future;
-  }
-
-  public function execPassthru($pattern /* , ... */) {
-    $args = func_get_args();
-    if (phutil_is_windows()) {
-      $args[0] = 'hg '.$args[0];
-    } else {
-      $args[0] = 'HGPLAIN=1 hg '.$args[0];
-    }
-
-    return call_user_func_array('phutil_passthru', $args);
+    return array(
+      'HGPLAIN' => 1,
+    );
   }
 
   public function getSourceControlSystemName() {
diff --git a/src/repository/api/ArcanistRepositoryAPI.php b/src/repository/api/ArcanistRepositoryAPI.php
--- a/src/repository/api/ArcanistRepositoryAPI.php
+++ b/src/repository/api/ArcanistRepositoryAPI.php
@@ -404,7 +404,102 @@
     return $this->buildLocalFuture($args);
   }
 
-  abstract protected function buildLocalFuture(array $argv);
+  /**
+   * Provide the name of the VCS binary, like `'git'`, `'hg'` or `'svn'`.
+   *
+   * @return string Name of the VCS binary.
+   */
+  abstract protected function getBinaryName();
+
+  /**
+   * Provide environmental variables specific to this VCS.
+   *
+   * These variables will be passed to VCS subprocesses. For example, Mercurial
+   * needs to execute with HGPLAIN.
+   *
+   * @return map<string, string> Map of environmental variables to pass to
+   *   VCS subprocesses.
+   */
+  protected function getExecutionEnvironment() {
+    return array();
+  }
+
+  final protected function getCommonExecutionEnvironment() {
+
+    // The name of the "English, UTF-8" locale varies across systems. Try to
+    // identify the correct name on this system.
+    static $locale = null;
+    if ($locale === null) {
+      list($err, $locales) = exec_manual('locale -a');
+      if ($err) {
+        // If we don't have `locale`, we're probably on Windows? This might
+        // not be the right thing to do?
+        $locale = 'en_US.UTF-8';
+      } else {
+        $locales = phutil_split_lines($locales, $retain_endings = false);
+        $locales = array_fuse($locales);
+
+        $try = array(
+          'en_US.utf8',
+          'en_US.UTF-8',
+        );
+
+        foreach ($try as $try_locale) {
+          if (isset($locales[$try_locale])) {
+            $locale = $try_locale;
+            break;
+          }
+        }
+
+        if ($locale === null) {
+          throw new Exception(
+            pht(
+              'Unable to find a valid English UTF-8 locale on this system. '.
+              'One of these locales is required: %s. These locales were '.
+              'found: %s.',
+              implode(', ', $try),
+              implode(', ', $locales)));
+        }
+      }
+    }
+
+    return array(
+      'LANG' => $locale,
+    );
+  }
+
+  protected function buildLocalFuture(array $argv) {
+    list($command, $env) = $this->formatVCSCommand($argv);
+
+    return id(new ExecFuture('%C', $command))
+      ->setEnv($env)
+      ->setCWD($this->getPath());
+  }
+
+  public function execPassthru($pattern /* , ... */) {
+    $argv = func_get_args();
+    list($command, $env) = $this->formatVCSCommand($argv);
+
+    // For passthru commands, we never parse the output and it's desirable
+    // to show it in the user's preferred language.
+    unset($env['LANG']);
+
+    $passthru = new PhutilExecPassthru('%C', $command);
+    $passthru->setEnv($env);
+    $passthru->setCWD($this->getPath());
+
+    return $passthru->execute();
+  }
+
+  private function formatVCSCommand(array $argv) {
+    $argv = call_user_func_array('csprintf', $argv);
+    $command = csprintf('%s %C', $this->getBinaryName(), $argv);
+
+    $env = $this->getExecutionEnvironment() +
+           $this->getCommonExecutionEnvironment();
+
+    return array($command, $env);
+  }
 
   public function canStashChanges() {
     return false;
diff --git a/src/repository/api/ArcanistSubversionAPI.php b/src/repository/api/ArcanistSubversionAPI.php
--- a/src/repository/api/ArcanistSubversionAPI.php
+++ b/src/repository/api/ArcanistSubversionAPI.php
@@ -36,13 +36,8 @@
     return $svn_dir;
   }
 
-  protected function buildLocalFuture(array $argv) {
-
-    $argv[0] = 'svn '.$argv[0];
-
-    $future = newv('ExecFuture', $argv);
-    $future->setCWD($this->getPath());
-    return $future;
+  protected function getBinaryName() {
+    return 'svn';
   }
 
   protected function buildCommitRangeStatus() {
diff --git a/src/workflow/ArcanistCommitWorkflow.php b/src/workflow/ArcanistCommitWorkflow.php
--- a/src/workflow/ArcanistCommitWorkflow.php
+++ b/src/workflow/ArcanistCommitWorkflow.php
@@ -142,23 +142,10 @@
     $tmp_file = new TempFile();
     Filesystem::writeFile($tmp_file, $message);
 
-    $command = csprintf(
-      'svn commit %Ls --encoding utf-8 -F %s',
-      $files,
-      $tmp_file);
-
-    // make sure to specify LANG on non-windows systems to suppress any fancy
-    // warnings; see @{method:getSVNLangEnvVar}.
-    if (!phutil_is_windows()) {
-      $command = csprintf('LANG=%C %C', $this->getSVNLangEnvVar(), $command);
-    }
-
-    chdir($repository_api->getPath());
-
-    $err = phutil_passthru('%C', $command);
-    if ($err) {
-      throw new Exception("Executing 'svn commit' failed!");
-    }
+    $err = $repository_api->execPassthru(
+      'commit --encoding utf-8 -F %s -- %Ls',
+      $tmp_file,
+      $files);
 
     $mark_workflow = $this->buildChildWorkflow(
       'close-revision',
@@ -273,32 +260,6 @@
     return array('svn');
   }
 
-  /**
-   * On some systems, we need to specify "en_US.UTF-8" instead of "en_US.utf8",
-   * and SVN spews some bewildering warnings if we don't:
-   *
-   *   svn: warning: cannot set LC_CTYPE locale
-   *   svn: warning: environment variable LANG is en_US.utf8
-   *   svn: warning: please check that your locale name is correct
-   *
-   * For example, it happens on epriestley's Mac (10.6.7) with
-   * Subversion 1.6.15.
-   */
-  private function getSVNLangEnvVar() {
-    $locale = 'en_US.utf8';
-    try {
-      list($locales) = execx('locale -a');
-      $locales = explode("\n", trim($locales));
-      $locales = array_fill_keys($locales, true);
-      if (isset($locales['en_US.UTF-8'])) {
-        $locale = 'en_US.UTF-8';
-      }
-    } catch (Exception $ex) {
-      // Ignore.
-    }
-    return $locale;
-  }
-
   private function runSanityChecks(array $revision) {
     $repository_api = $this->getRepositoryAPI();
     $revision_id = $revision['id'];