From LimeSurvey Manual
There are two places where language specific localization are defined and stored.
One is in the Installation directory where built-in messages to the PHP code are stored in language specific files. These must be translated and installed by the system administrator before that language is available for the administrative interface and for some basic buttons and built-in messages seen by survey participants. Normally, a survey developer would not have access to edit but only select these translations.
The other source of language specific localization is in the surveys themselves. These translations for each survey consist of the survey title, overview, and each group, question, answer and labelset text. All these translations are stored in the SQL database tables themselves. Normally, a survey developer must define all the desired translations beyond the base language.
Languages for administration interface and built-in messages for survey participants
The public survey screens and the admin interface can be localized so that built-in messages and text will appear in your preferred language. For example "yes" and "no" would appear as "ja" and "nein" in the Deutsch/German version. LimeSurvey has about 50 different languages of built-in messages already translated. To see the translation status for these languages please follow the link:
You can create/update your own translation locally by using these instructions:
If you want to update an existing translation, please consider contributing it for future releases (Read: Translations Status). If you only update your version, remember to take care of this when you upgrade later.
So far we only discussed translating the built-in text of the administration interface that the survey participants and developers see; that part that is independent of any survey. Each survey can have one or more languages associated with it as well independent of this interface. So care must be taken to offer the appropriate translations there as well.
Languages for surveys themselves
If more than one language is defined for a survey, then when editing that survey or each question, answer or labelset within it -- you then need to make sure to add all the language translations desired. Otherwise, the default language of the survey will appear if no translation is available. This is available when editing a Survey, Group, Question, Answer set or labelset.