Add German Umlauts

[salcode]

In this fork by @F10WB0T, German Umlauts are added ( and some of my indentations are fixed 😀 ).

It makes sense to add those improvements here, as well.

Along with this we should add a test string that uses Umlauts in fe_sanitize_title_js_shortcode().

[salcode]

The following seems like a reasonable string to use when testing these characters,
Ä ä Ö ö Ü ü ß.

When this string is processed with WordPress's PHP sanitize_title() function, the result is
a-a-o-o-u-u-s

As a reminder, the goal of this project is to get the same behavior in JavaScript that we get from WordPress's PHP sanitize_tilte().

Currently, our JavaScript code renders this string as
ae-ae-oe-oe-ue-ue-ss

Correction: Our current JavaScript code does seem to render this test string the same as the WordPress PHP function sanitize_title().

I determined this by adding the [sanitize-title-js] shortcode, where renders the test string with PHP and JavaScript.

Both rendered a-a-o-o-u-u-s

@F10WB0T, if you run the PHP code echo sanitize_title('Ä ä Ö ö Ü ü ß'); do you get the same a-a-o-o-u-u-s?

If not, I wonder if this could be affected by WordPress localization.

[F10WB0T]

@salcode, that's interesting. I think it's just as you assumed. The WordPress localization is affecting this function. When I run echo sanitize_title('Ä ä Ö ö Ü ü ß'); I get ae-ae-oe-oe-ue-ue-ss. But when I switch the site language to English I get a-a-o-o-u-u-s.

[salcode]

Thanks for checking that out @F10WB0T, I'm not sure how best to handle this.

A couple of different thoughts cross my mind.

1. Turn this whole thing into an AJAX call to WordPress and use the WordPress PHP sanitize_title() to do the work and return the value.
2. Pass the localization language into the JavaScript function and add conditional language based logic there.
3. Add an additional parameter to our JavaScript wpFeSanitizeTitle() function, to allow sending a custom mapping. e.g.

wpFeSanitizeTitle(
    'My string to sanitize',
    {
         {'base':'AE','letters':'\u00c4'},
         {'base':'OE','letters':'\u00d6'}
    }
);

Right now, I'm leaning towards the 3rd option. I realize this isn't a significant improvement to your use-case. At this point, you're probably best off using your fork.

[salcode]

For now, this project is going emulate sanitize_title() when the Site Language is English (United States). I've made a note of this in the wiki.

A big thanks to @F10WB0T for bringing this behavior to my attention.