Can you please describe a scenario in more detail? I am having trouble following the actual consequences of the bug you are reporting.

I'm experiencing the same issue.

Here's a (lengthy) account of what happened for me:

• At first, the default language for my Mantis instance was set to 'english'. I had created a custom_strings_inc.php file, with both English and French translations. As I intended French to eventually be the default language, my custom_strings_inc.php looked like this :

<?php
if ( lang_get_current() == 'english' ) {
$s_call_type = 'Call type';
...
} else {
// Default (French is set as the default language)
$s_call_type = 'Type d\'appel';
...
}
?>

Everything worked fine under this setup.

• Then I changed the default language to 'french' in config_inc.php.
  For users that use French, everything works still fine. Custom field labels (and everything else) are displayed in French.
  However, for users that have chosen English as their language, custom field labels are still displayed in French, even though the rest of the page is displayed in English.

I have tried to locate where the error lies, and it seems that when lang_get_current() is evaluated in custom_strings_inc.php, it returns 'french' instead of 'english' for English-speaking users (just as phu reported).
Investigating a bit further, I narrowed down the problem to lang_get_default() in lang_api.php, on line 98:

if( function_exists( 'auth_is_user_authenticated' ) && auth_is_user_authenticated() ) {
    $t_lang = user_pref_get_language( auth_get_current_user_id() );
}

This snipped returns the correct language most of the time, but in this particular issue, it fails to return 'english' when evaluating the current language in custom_strings_inc.php. The default language ('french') is then chosen as a fallback, causing the custom fields to be translated into the wrong language.

I have the same problem with 1.2.8 I think. Will test the issue with 1.2.10 and post again, if problem still exists.

The problem is caused by using an incorrect method to determine the current language in custom_strings_inc.php.

The example in the MantisBT documentation advised to use lang_get_current() to determine the current language, but this function resets the active language, and therefore returns an incorrect value when the default language ($g_default_language) is different from English.

The proper method is to use the global variable $g_active_language, as per the example below:

<?php

switch( $g_active_language ) {

case 'french':

$s_my_start_date = 'Date de début';

break;

default:
    # Default language, as defined in config_inc.php
    # ($g_default_language, English in this case)
    $s_my_start_date = 'Start Date';
    break;
}

The documentation has been updated accordingly.

Marking as 'acknowledged' not resolved/closed to track that change gets ported to master-2.0.x branch