Fix #15558: url_get() fallback to next method in case of error
Localisation updates from http://translatewiki.net.
Fix invalid access denied error caused by access_has_bug_level()

Commit d42e80c01277eec37c7436a23ec72073c9961c49 changed the code in
access_has_bug_level() function, and introduced a bug in the call to
access_compare_level() when access is limited to issue reporter
(inverted parameters caused an incorrect access denied error).

See also 9ec47a056156ac32e1f95cd0ec20d4db8bd54d3b.

Issue #15538
Print pages: don't show custom fields user has no access to

Prior to this, if a custom field's 'read' access level were higher than
the user's access, the print pages would display the field's label (but
not the data). This behavior is not consistent with how this situation
is handled in the View Issue page, where the field is not shown at all.

For consistency, we now skip the of the custom field users have no read
access to in the print pages, so that nothing is displayed.

Fixes #15528
Documentation: added php_mbstring as recommended extension

Fixes #15575