remove_accents() can't handle Vietnamese vowels

[tgeorge]

replace_accents() can't handle many of the vowels present in Vietnamese. For the complete list of vowels:

​http://en.wikipedia.org/wiki/Vietnamese_alphabet#Tone_marks

Here are the precise vowels that replace_accents() can't handle currently:

ẰằẦầỀềỒồỜờỪừỲỳẢảẲẳẨẩẺẻỂểỈỉỎỏỔổỞởỦủỬửỶỷẴẵẪẫẼẽỄễỖỗỠỡỮữỸỹẮắẤấẾếỐốỚớỨứẠạẶặẬậẸẹỆệỊịỌọỘộỢợỤụỰựỴỵ

And here are those same vowels without accents:

AaAaEeOoOoUuYyAaAaAaEeEeIiOoOoOoUuUuYyAaAaEeEeOoOoUuYyAaAaEeOoOoUuAaAaAaEeEeIiOoOoOoUuUuYy

I meant "remove_accents()", not "replace_accents()". Sorry! The "remove_accents()" function is defined in formatting.php.

There are four additional vowels that remove_accents() can't handle. I forgot them in my original message:

ƠơƯư

And here are those same vowels without accents:

OoUu

I've made a patch, but it's a huge chunk of characters, and I wonder if this should rather be included into Vietnamese package as a filter.

Perhaps remove_accents() needs a filter for this, so that replacements in sanitize_title() could only occur with save context.

Replying to SergeyBiryukov:

Perhaps remove_accents() needs a filter for this, so that replacements in sanitize_title() could only occur with save context.

remove_accents() is already only called there on save context, so this should be good.

I meant hooking into sanitize_title() from wp-content/languages/vi.php.
I missed that context is passed to sanitize_title filter, so that's currently possible too.

Add unit tests, this patch works on its own, but probably should be incorporated into the tests in #9591

Updated tests

Updated tests to apply to ​[UT 471]

Before patch: Tests: 12, Assertions: 13, Failures: 6.

With attachment:17738.patch​ OK (12 tests, 13 assertions)

When version is 3.1.3 and the ticket needs-unit-tests it is not going to make 3.3. Punting.

Per IRC chat, it's better to keep the keyword until the tests are reviewed and committed.

​[UT663]

In [20687]:

Add Vietnamese vowels to remove_accents(). props SergeyBiryukov. fixes #17738.