Sandbox

SELECT 
  pfv.variant_id, 
  pfv.position, 
  pfvd.variant 
FROM 
  cscart_product_feature_variants AS pfv 
  INNER JOIN cscart_product_feature_variant_descriptions AS pfvd ON pfv.variant_id = pfvd.variant_id 
  AND pfvd.lang_code = 'en' 
WHERE 
  pfv.variant_id IN (1198, 1199, 1200, 1201)

Query time 0.00043

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	pfvd	range	PRIMARY	PRIMARY	9		4	Using index condition
1	SIMPLE	pfv	eq_ref	PRIMARY	PRIMARY	3	cscart_dev_4_16.pfvd.variant_id	1

Result

variant_id	position	variant
1198	1	Green
1199	2	Blue
1200	3	Black
1201	4	White