Same problem!!! Impossible upgrade or install language after removing.
How to manual install language??? After unzipping language file content to /oc-content/languages/xx-XX its stil not present on dashbuard. Dashbuard showing on top "1 Language update", but language is removed.
After enabling debug, no errors?
OsClass 8.1.1
PHP 7.4.3
Zip version 1.15.6
Libzip headers version 1.5.1
Libzip library version 1.5.1
P.S. maybe its same error on utils.php when i try make web site backup ===> PHP Warning: ZipArchive::close(): Can't open file: Permission denied in /var/www/html/domain.xx/oc-includes/osclass/utils.php on line 1413, referer:
https://www.domain.xx/oc-admin/index.php?page=tools&action=backup=========== Resolved =====
Its bad archive of language zip file (20230411_lang_osclass_ru_RU_8.1.1.zip). After downloading manually language file, unzip and zip again the installation success!