How to use spell checking in PO mode for gettext translations files?

I've tried function I use my my Markdown and Polymode when editing my Jekyll blog with po-mode but it don't work at all:

I have code like this:

(defun lang (lang) (interactive "sLanguage: ") (ispell-change-dictionary lang) (flyspell-buffer)) 

when I run lang polish it process the file but nothing happen even if do error in one the translation.

I was looking at https://www.emacswiki.org/emacs/PoMode

but this don't work.

How can I get error checking inside PO file so I know that I need to edit the entry and fix the error.

It would also be nice to have error checking while editing.