Hi
I use SilverStripe CMS - 2.4.2 with Forum module 0.3-r113106
In my site config I use

Object::add_extension('SiteTree', 'Translatable');
Translatable::set_default_locale('uk_UA');

In folder forum/lang I create file uk_UA.php

<?php
i18n::include_locale_file('modules: forum', 'en_US');

global $lang;

if(array_key_exists('uk_UA', $lang) && is_array($lang['uk_UA'])) {
	$lang['uk_UA'] = array_merge($lang['en_US'], $lang['uk_UA']);
} else {
	$lang['uk_UA'] = $lang['en_US'];
}
............................

But SilverStripe not see my file, connects only English lang file.
Tell me how to make the forum work with my localization?

did you do a flush?

yes