Since a year and across several updates, for a few surveys (in the magintude 1 out of 100), the following error occurs sometimes for some users when they list their surveys in the admin panel:

500: Internal server error - Survey language settings (de) not found. Please run the integrity check from the main menu.

As suggested, running the integrity check from main menu is not viable because our tables are much too huge, which leads to a request timeout.

When the sysadmin searches for the affected user in the web UI to list the user's surveys, also the admin will be presented the same error message.

The fix is definitely the following.

First, determine if this is really the problem:

SELECT COUNT(*) AS broken_surveys
FROM lime_surveys s
LEFT JOIN lime_surveys_languagesettings sl
  ON s.sid = sl.surveyls_survey_id
 AND s.language = sl.surveyls_language
WHERE sl.surveyls_survey_id IS NULL;

If this does not show "0", then the mentioned problem occurs. This happend several times for us.

Determine if the reporting user is affected:

SELECT s.sid, s.owner_id, u.users_name, u.full_name, s.language
FROM lime_surveys s
JOIN lime_users u on s.owner_id = u.uid
WHERE s.sid IN (
  SELECT s.sid
  FROM lime_surveys s
  LEFT JOIN lime_surveys_languagesettings sl
    ON s.sid = sl.surveyls_survey_id
   AND s.language = sl.surveyls_language
  WHERE sl.surveyls_survey_id IS NULL
)
ORDER BY owner_id;

Fix the problem for all users in one go:

INSERT INTO lime_surveys_languagesettings
(
  surveyls_survey_id,
  surveyls_language,
  surveyls_title
)
SELECT
  sid,
  language,
  CONCAT('Recovered survey ', sid)
FROM lime_surveys s
WHERE NOT EXISTS (
  SELECT 1
  FROM lime_surveys_languagesettings sl
  WHERE sl.surveyls_survey_id = s.sid
    AND sl.surveyls_language = s.language
);

Re-check with the following steps above (web UI and the two SELECT-queries), the issue should be gone.