SELECT 
  tax 
FROM 
  cscart_tax_descriptions 
WHERE 
  tax_id = 6 
  AND lang_code = 'en'

Query time 0.00018

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_tax_descriptions const PRIMARY PRIMARY 9 const,const 1

Result

tax
VAT