[core] Decode environment variables with filesystem encoding (Fixes #3854, Fixes #3217, Fixes #2918)

Introduces compat versions of os.getenv and os.path.expanduser

test/test_utils.py

@@ -44,6 +44,9 @@ from youtube_dl.utils import (
     limit_length,
     escape_rfc3986,
     escape_url,
+    get_filesystem_encoding,
+    compat_getenv,
+    compat_expanduser,
 )
 
 
@@ -331,5 +334,15 @@ class TestUtil(unittest.TestCase):
         )
         self.assertEqual(escape_url('http://vimeo.com/56015672#at=0'), 'http://vimeo.com/56015672#at=0')
 
+    def test_compat_getenv(self):
+        test_str = 'тест'
+        os.environ['YOUTUBE-DL-TEST'] = test_str.encode(get_filesystem_encoding())
+        self.assertEqual(compat_getenv('YOUTUBE-DL-TEST'), test_str)
+
+    def test_compat_expanduser(self):
+        test_str = 'C:\Documents and Settings\тест\Application Data'
+        os.environ['HOME'] = test_str.encode(get_filesystem_encoding())
+        self.assertEqual(compat_expanduser('~'), test_str)
+
 if __name__ == '__main__':
     unittest.main()