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SELECT 
  a.*, 
  b.description 
FROM 
  cscart_currencies as a 
  LEFT JOIN cscart_currency_descriptions as b ON a.currency_code = b.currency_code 
  AND lang_code = 'en' 
WHERE 
  1 
  AND a.is_primary = 'Y' 
ORDER BY 
  a.position

Query time 0.00026

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	a	ALL					5	Using where; Using filesort
1	SIMPLE	b	eq_ref	PRIMARY	PRIMARY	38	mahm3t_cs443.a.currency_code,const	1	Using where

Result

currency_code	after	symbol	coefficient	is_primary	position	decimals_separator	thousands_separator	decimals	status	currency_id	description
PLN	Y	zł	1.00000	Y	2	,	.	2	H	3	PLN