Hi! I am about to translate the board into Bulgarian and I just wanted to make sure I am doing it correctly. I open the lng file and then I translate all words between ' and ' right? Thanks in advance

Yepp. you're right

In the end of the file lang\eng.php ,I met some difficulties.Becaue they are the words from old version.I am a newbie and haven't used the old version.Please help me.
Here are problems:
/* Language variables miniBB v1.1 */

$l_unsubscribe='Unsubscribe';
^^^^^^^^^^^^
<<--what's the meaning of unsubscribe in miniBB.Do you mean to subscribe money?
$l_member='Member';

/* Language variables miniBB v1.2 */
$l_searchUsers='Search users';
$l_haventReg='Haven`t made new posts since YYYY-MM-DD';
$l_wrongData='Incorrect input!';
$l_recordsFound='Record(s) found:';
^^^^^^^^^^^^^^^^
<<--What record are found?
$l_inactiveUsers='Inactive users (haven`t posted anything)';
$l_subscriptions='Subscriptions';
^^^^^^^^^^^^^
<<--What's the meaning?

/* Language variables miniBB v1.3 */

$l_days='days';
$l_days_within='Within last';
^^^^^^^^^^^
<<--what is within last?Topics?
$l_stats_days_c='This setting affects only most popular topics and most viewed topics.';
$l_search[11]='Match whole words';
$l_privateForum='You don`t have access to this forum.';
$l_moderator='Moderator';
^^^^^^^^^^
<<--Could you give the detail about moderator's meaning in the forum?
$l_moderatorsAre='Forums moderator(s)';

/* Language variables miniBB v1.5 */
$l_makeSticky='Make sticky';
$l_makeUnsticky='Make unsticky';
$l_topicSticked='Topic was sticked';
$l_topicUnsticked='Topic was unsticked';
?>

Unsubscribe means unsubscribe from letter (as I see, for example, you are subscribed to receive messages to an email when someone replies).

Record(s) found - database records.

Subscriptions - the link for administrator, clicking on it, admin can see the list of subscribed users to the topic.

"Within last" - simply the general phrase. Used with combination of "days" so because it is splitted by input text field (see in search and statistics).

Moderator is the person with high privileges level, similar to admin, who can edit, delete and move any topics and posts, but can not enter the admin panel.