SELECT 
  s.title, 
  d.descr 
FROM 
  cscart_unit_price_descr d 
  INNER JOIN cscart_unit_prices s ON s.unit_price_id = d.unit_price_id 
WHERE 
  s.unit_price_id = 1 
  AND d.lang_code = 'en' 
  AND s.status = 'A'

Query time 0.00026

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE d const unit_price_id unit_price_id 10 const,const 1
1 SIMPLE s const PRIMARY PRIMARY 4 const 1

Result

title descr
m² m²