From LimeSurvey Manual
In some cases, the administrator might not want to give a user (e.g., a single-survey translator) global permissions because they would then be able to access all the surveys. For this purpose, the survey permissions panel was created - to facilitate the allocation of permissions to different users without the need of using the global system of permissions. As a result, the translator can be allocated certain permissions that would allow them to edit only certain surveys.
To use the survey-restricted permissions system, click the Survey permissions button located on the Settings menu.