Localisation updates from http://translatewiki.net.
Tests: move include of constant_inc.php to SoapBase.php
Remove useless variable initialization

Follow up fix on commit ec5397514cd2e96eb8dfba4b9940ab8c0cde1d49
Fix #16187: error caused by array_combine() with PHP<5.4

array_combine() function behavior was changed in PHP 5.4 [1]; in earlier
versions it would issue a warning and return false when working with
empty arrays, which then causes Mantis to trigger an application error.

This is a regression introduced by cc7703acc8d05f253d52a152a7d8cd0c1c43815d

[1] http://php.net/function.array-combine.php
Fix #16158: mc_filter_get_issues does not populate monitors fiels for
retrieved issues
Localisation updates from http://translatewiki.net.
soap api: make sure we have a compatible soap extension installed

Even though the soap extension is installed, versions of PHP older than
5.2.2 do not support all the features we need. To guard against
unexpected errors, we now enable the soap extension if the
SOAP_USE_XSI_ARRAY_TYPE constant is defined. This constant is used at
runtime by the SOAP extension and is a good indicator of a recent enough
soap extension.

Fixes #16252: API SOAP provides no answer after MantisBT upgrade
Do not redirect after creating the first project

When the first project is created after installing MantisBT, an
application error 2800 occurs when submitting the changes from
manage_proj_create_page.php, although the project is created
successfully.

Regression introduced by b1a1bbaeb690b7611899ae8075586d655155d18c

Fixes #16337
Translate custom field names

Custom fields are displayed with their name, disregarding their
localization :
- in the history log
- in the custom fields section, in the project management page

Thanks to jmonin for the patch.

Fixes #12470