After the renaming of the language codes sr-ec and sr-el to sr-cyrl and sr-latn by change I75da0af35a2066e7963e50c56c99daf1e07c55e6 (https://gerrit.wikimedia.org/r/c/mediawiki/core/+/251312) the user options in the database still contains the old values sr-ec and sr-el. On reading of the user options the deprecated language codes get automatically replaced by T131042: Replace deprecated language codes in user options. Therefor the intended user settings still works.

But at some time the user options in the database should be cleaned up. This can be done by

$ maintenance/userOptions.php --old sr-ec --new sr-cyrl language
$ maintenance/userOptions.php --old sr-el --new sr-latn language
$ maintenance/userOptions.php --old sr-ec --new sr-cyrl variant
$ maintenance/userOptions.php --old sr-el --new sr-latn variant
$ maintenance/userOptions.php --old sr-ec --new sr-cyrl variant-sr
$ maintenance/userOptions.php --old sr-el --new sr-latn variant-sr