Do not install unwanted locales.

--- a/setup.py	2014-11-01 11:21:49.679613605 +0100
+++ b/setup.py	2014-11-01 11:26:36.305719135 +0100
@@ -101,9 +101,15 @@
 
 PO_DIR = 'po'
 MO_DIR = os.path.join('build', 'po')
+LINGUAS = os.environ.get('LINGUAS', '*').split(' ')
 
 for po in glob.glob(os.path.join(PO_DIR, '*.po')):
     lang = os.path.basename(po[:-3])
+
+    # Skip unwanted locales
+    if lang not in LINGUAS and '*' not in LINGUAS:
+        continue
+
     mo = os.path.join(MO_DIR, lang, 'gtg.mo')
     target_dir = os.path.dirname(mo)
     if not os.path.isdir(target_dir):
