String encapsulation for improved translation

I just realized that my suggestion is a bit short-sighted without investigating what the original does. In regular C's `printf()` the format string for `%` is `%%`, so that'd make a regexp of `[^%]%[0-9]`. Does the same apply to Qt's? It doesn't specify in [the documentation](http://qt-project.org/doc/qt-5/qstring.html#arg). However, it does offer this:

> Place marker numbers must be in the range 1 to 99.

In other words, tentatively this'd be the regexp:
```lua
[^%]%[1-9][0-9]?
```