[StGaensler]

Don't use tborder - its on the same "level" as stg_table and stg_table_test.

These lines should do it (first for all tables, second for your new class):

.stg_table {border: 1px solid #000; padding: 5px;}
.stg_table_table {border: 1px solid #000; padding: 5px;}

Uninstalling the language: I don't know a vBulletin function for that. A way could be to use AdminCP -> Language & Phrases -> Phrase Manager -> [Find orphan Phrases] Delete all phrases containing stg_table and the phrase settinggroup_bbcode_table

Stefan