LimeSurvey 1.x navigating the source code
From LimeSurvey Manual
After downloading the source code via SVN (See: Accessing the Source Code) you see the following directories:
Source
/limesurvey
This is the current stable branch of LimeSurvey and contains the latest hotfixes and translation updates.
/original art
This is the directory with the original arts used in LimeSurvey.
/server-scripts
In this directory are server scripts which are in use in http://www.limesurvey.org .
releases
In this directory are the files, as they are delivered in the download package of the according version.
Code
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Translations
To translate some text displayed on screen you have to either create a new instance of 'limesurvey_lang' (limesurvey\classes\core\language.php) or in some cirumstances there is already an instance created called '$clang'.
To translate you call the function gT ($clang->gT(string)). More information on how to use localization can be found here.
In general $clang is set in (limesurvey\common.php) and uses a number of variables to determine language.
s_lang
$baselang
$_SESSION['adminlang']