PICARD-2386: Fix sorting of characters with diacritics

Columns in main list which were not using natural sorting had all characters with diacritics sorted after Z. Use locale.strxfrm for locale aware sorting instead.

picard/ui/itemviews.py

@@ -47,6 +47,7 @@ from heapq import (
     heappop,
     heappush,
 )
+from locale import strxfrm
 
 from PyQt5 import (
     QtCore,
@@ -919,9 +920,9 @@ class TreeItem(QtWidgets.QTreeWidgetItem):
         if column == MainPanel.LENGTH_COLUMN:
             sortkey = self.obj.metadata.length or 0
         elif column in MainPanel.NAT_SORT_COLUMNS:
-            sortkey = natsort.natkey(self.text(column).lower())
+            sortkey = natsort.natkey(self.text(column))
         else:
-            sortkey = self.text(column).lower()
+            sortkey = strxfrm(self.text(column))
         self._sortkeys[column] = sortkey
         return sortkey