There appears to be a problem with the PO file

'LC_MESSAGES/editors/3dview/grease_pencil/stroke_edit.po'

Where the comment is duplicated and one of it (top line) doesn't have a linenumber reference at the end:

#: ../../manual/editors/3dview/grease_pencil/stroke_edit.rst
#: ../../manual/editors/3dview/grease_pencil/stroke_edit.rst:76
msgid "Menu"
msgstr "Trình Đơn -- Menu"

This is causing sphinx to abort with error upon write (dump_po) in the file

• '.local/lib/python3.6/site-packages/sphinx_intl/catalog.py'
• '.local/lib/python3.6/site-packages/babel/messages/pofile.py'

Exception occurred:

File ".local/lib/python3.6/site-packages/babel/messages/pofile.py", line 592, in write_po
  for filename, lineno in sorted(message.locations):

TypeError: '<' not supported between instances of 'int' and 'NoneType'

The problem is caused by the line

sorted(message.locations)

since it was expecting to see that there is a line number (int) and not 'None', due to the missing number. This is happening with every language sets.