storage: Fix issue with locales that use other decimal separators

- Convert commas to periods
- Convert arabic decimal operator instead to period

Signed-off-by: Johannes Keyser <johanneskeyser@posteo.de>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/storage/views.py

@@ -104,6 +104,8 @@ def warn_about_low_disk_space(request):
 
 def _interpret_size_string(size_str):
     """Convert size string to number of bytes."""
+    size_str = size_str.replace(',', '.')  # some locales use commas
+    size_str = size_str.replace('٫', '.')  # arabic decimal separator
     if size_str[-1] in '0123456789':
         return float(size_str[:-1])