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SELECT 
  a.variant_id, 
  a.option_id, 
  a.position, 
  a.modifier, 
  a.modifier_type, 
  a.weight_modifier, 
  a.weight_modifier_type, 
  b.variant_name, 
  IF(
    shared_option_variants.variant_id IS NOT NULL, 
    shared_option_variants.modifier, 
    a.modifier
  ) as modifier, 
  IF(
    shared_option_variants.variant_id IS NOT NULL, 
    shared_option_variants.modifier_type, 
    a.modifier_type
  ) as modifier_type 
FROM 
  cscart_product_option_variants as a 
  LEFT JOIN cscart_product_option_variants_descriptions as b ON a.variant_id = b.variant_id 
  AND b.lang_code = 'de' 
  LEFT JOIN cscart_ult_product_option_variants shared_option_variants ON shared_option_variants.variant_id = a.variant_id 
  AND shared_option_variants.company_id = 1 
WHERE 
  a.option_id IN (625) 
  AND a.status = 'A' 
ORDER BY 
  a.position, 
  a.variant_id

Query time 0.00070

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	a	ref	status,option_id,option_id_2	option_id	6	const,const	7	Using index condition; Using where; Using filesort
1	SIMPLE	b	eq_ref	PRIMARY	PRIMARY	9	mahm3t_cs443.a.variant_id,const	1	Using where
1	SIMPLE	shared_option_variants	eq_ref	PRIMARY,company_id	PRIMARY	7	mahm3t_cs443.a.variant_id,const	1

Result

variant_id	option_id	position	modifier_type	weight_modifier_type	variant_name
15192	625	100	A	A	55x100 h=280 cm
15194	625	210	A	A	60x100 h=280 cm
15196	625	230	A	A	60x120 h=280 cm
15198	625	241	A	A	60x130 h=305 cm
15201	625	310	A	A	70x100 h=280 cm
15202	625	330	A	A	70x120 h=280 cm
15203	625	340	A	A	70x130 h=280 cm
15204	625	341	A	A	70x130 h=305 cm
15205	625	350	A	A	70x140 h=280 cm
15206	625	351	A	A	70x140 h=305 cm
24201	625	352	A	A	80x120 h=280 cm