Catch more Python errors

Noticed these days a couple of errors we don't catch:
* variables with format ```%s```
* ```%%``` (we have one in history-details.lang, caught last week for one locale)

This is currently showing 2 errors for Hebrew, I wonder if the first one is actually an error (I think so, and also the string seems unused, PHP stuff?).
```
;Except where otherwise <a href="%s">noted</a>, content on this site is licensed under the <br /><a href="%s">Creative Commons Attribution Share-Alike License v3.0</a> or any later version.
התוכן באתר זה הנו תחת רישיון <a href="%2$s">Creative Commons Attribution Share-Alike License v3.0</a> או גרסאות מאוחרות יותר, אלא אם <a href="%1$s">צויין</a> אחרת.
```