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SELECT 
  lang.name, 
  IF(
    cscart_ult_language_values.value IS NULL, 
    lang.value, cscart_ult_language_values.value
  ) as value 
FROM 
  cscart_language_values lang 
  LEFT JOIN cscart_ult_language_values ON cscart_ult_language_values.name = lang.name 
  AND company_id = 1 
  AND cscart_ult_language_values.lang_code = lang.lang_code 
WHERE 
  lang.lang_code = 'en' 
  AND lang.name IN (
    'no_products_selected', 'all_features', 
    'all_features', 'similar_only', 
    'similar_only', 'different_only', 
    'different_only', 'clear_list', 
    'add_feature', 'add', 'compare', 
    'no_products_selected', 'all_features', 
    'all_features', 'similar_only', 
    'similar_only', 'different_only', 
    'different_only', 'clear_list', 
    'add_feature', 'add', 'compare'
  )

Query time 0.00043

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_ult_language_values	system	PRIMARY				0	const row not found
1	SIMPLE	lang	range	PRIMARY	PRIMARY	392		8	Using index condition

Result

name	value
add	Add
add_feature	Add feature
all_features	All features
clear_list	Clear list
compare	Compare
different_only	Different only
no_products_selected	No products selected
similar_only	Similar only