diff --git a/wagtail_localize/models.py b/wagtail_localize/models.py
index 07071622..722e8155 100644
--- a/wagtail_localize/models.py
+++ b/wagtail_localize/models.py
@@ -1252,8 +1252,11 @@ def import_po(
 
         for index, entry in enumerate(po):
             try:
+                # Filter by hash instead to avoid case sensitivity issues
+                # https://github.com/wagtail/wagtail-localize/issues/758
                 string = String.objects.get(
-                    locale_id=self.source.locale_id, data=entry.msgid
+                    locale_id=self.source.locale_id,
+                    data_hash=String._get_data_hash(entry.msgid),
                 )
                 context = TranslationContext.objects.get(
                     object_id=self.source.object_id, path=entry.msgctxt
diff --git a/wagtail_localize/views/edit_translation.py b/wagtail_localize/views/edit_translation.py
index ad45ccb6..e690f2e8 100644
--- a/wagtail_localize/views/edit_translation.py
+++ b/wagtail_localize/views/edit_translation.py
@@ -1,4 +1,5 @@
 import json
+import os
 import tempfile
 
 from collections import defaultdict
@@ -1328,20 +1329,25 @@ def upload_pofile(request, translation_id):
 
     do_import = True
 
-    with tempfile.NamedTemporaryFile() as f:
+    # Set delete to false. This fixes some windows errors when creating tempfiles.
+    # This is due to the Windows OS locking temporary files when open.
+    # https://github.com/wagtail/wagtail-localize/issues/757
+    with tempfile.NamedTemporaryFile(delete=False) as f:
         # Note: polib.pofile accepts either a filename or contents. We cannot pass the
         # contents directly into polib.pofile or users could upload a file containing
         # a filename and this will be read by polib!
         f.write(request.FILES["file"].read())
         f.flush()
 
-        try:
-            po = polib.pofile(f.name)
+    # Move indentation back, we should open the file outside of the with statement.
+    # Delete must be set to false, otherwise the file will be deleted before we can open it.
+    try:
+        po = polib.pofile(f.name)
 
-        except (OSError, UnicodeDecodeError):
-            # Annoyingly, POLib uses OSError for parser exceptions...
-            messages.error(request, _("Please upload a valid PO file."))
-            do_import = False
+    except (OSError, UnicodeDecodeError):
+        # Annoyingly, POLib uses OSError for parser exceptions...
+        messages.error(request, _("Please upload a valid PO file."))
+        do_import = False
 
     if do_import:
         translation_id = po.metadata["X-WagtailLocalize-TranslationID"]
@@ -1356,9 +1362,14 @@ def upload_pofile(request, translation_id):
 
     if do_import:
         translation.import_po(po, user=request.user, tool_name="PO File")
-
         messages.success(request, _("Successfully imported translations from PO File."))
 
+    # Delete the created tempfile
+    try:
+        os.unlink(f.name)
+    except OSError:
+        pass
+
     # Work out where to redirect to
     next_url = get_valid_next_url_from_request(request)
     if not next_url: