Which LD version are you running? All these language bits (same used in Pages) where removed in the upgrade to LD 5.4.0. Today LD doesn't has a category_desc lang bit; all category langs now use a prefix: links_, so now it is:
'links_category_desc' => 'Description',
'links_category_desc_placeholder' => 'Add a description',
If that's the only one in trouble, then just delete it directly in your SQL Toolbox:
delete from core_sys_lang_words where word_app = 'links' AND word_key = 'category_desc';
If you use prefix iin your tables, than add it to the table name. Example using prefix ibf_:
delete from ibf_core_sys_lang_words where word_app = 'links' AND word_key = 'category_desc';
If you have more lang bits in this situation and if you have access to FTP, then open the applications/links/setup/upg_500039/upgrade.php and you will see all the language bits removed in 5.4.0.
Let me know if you need help.