The list of languages to choose from in wp-admin is empty. Everywhere where there would be a list of available languages, it is empty.
Then while debugging the issue, the following error occurred.
WordPress database error for Expression #10 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'wordpress.lt.name' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by username
SELECT
l.code,
l.id,
english_name,
nt.name AS native_name,
major,
active,
default_locale,
encode_url,
tag,
lt.name AS display_name
FROM wp_icl_languages l
JOIN wp_icl_languages_translations nt
ON ( nt.language_code = l.code AND nt.display_language_code = l.code )
LEFT OUTER JOIN wp_icl_languages_translations lt ON l.code=lt.language_code
WHERE
( lt.display_language_code = 'sv'
OR (lt.display_language_code = 'en'
AND NOT EXISTS ( SELECT *
FROM wp_icl_languages_translations ls
WHERE ls.language_code = l.code
AND ls.display_language_code = 'sv' ) ) )
GROUP BY l.code
ORDER BY english_name ASC skapat av WPML_Installation::refresh_active_lang_cache
Solution:
The problem was the wrong SQL setting. For an unknown reason, the sql_mode option had been set tp only_full_group_by. This is wrong. In fact, WordPress itself automatically unsets these incompatible SQL modes, without intervention. Please see the source code here.
