PICARD-1633: fix system locale detection on macOS

This failed due to:
- macOS returning language / country separated by "-" instead of "_" (en-UK instead of en_UK)
- required pyobjc modules not being packaged

picard/i18n.py

@@ -63,6 +63,7 @@ def setup_gettext(localedir, ui_language=None, logger=None):
                 import Foundation
                 defaults = Foundation.NSUserDefaults.standardUserDefaults()
                 current_locale = defaults.objectForKey_('AppleLanguages')[0]
+                current_locale = current_locale.replace('-', '_')
                 locale.setlocale(locale.LC_ALL, current_locale)
             except Exception as e:
                 logger(e)

requirements-macos.txt

@@ -1,3 +1,5 @@
 discid==1.2.0
 mutagen==1.42.0
+pyobjc-core==5.2
+pyobjc-framework-Cocoa==5.2
 PyQt5==5.13.1