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 (
    'stay_connected', 'exclusive_promotions_short', 
    'exclusive_promotions_content_short', 
    'subscribe', 'stay_connected', 'exclusive_promotions_short', 
    'exclusive_promotions_content_short', 
    'subscribe'
  )

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.01204264,
    "nested_loop": [
      {
        "table": {
          "table_name": "lang",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "392",
          "used_key_parts": ["lang_code", "name"],
          "loops": 1,
          "rows": 4,
          "cost": 0.00764568,
          "filtered": 100,
          "attached_condition": "lang.lang_code = 'en' and lang.`name` in ('stay_connected','exclusive_promotions_short','exclusive_promotions_content_short','subscribe','stay_connected','exclusive_promotions_short','exclusive_promotions_content_short','subscribe')"
        }
      },
      {
        "table": {
          "table_name": "cscart_ult_language_values",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "396",
          "used_key_parts": ["lang_code", "name", "company_id"],
          "ref": ["lvshop.lang.lang_code", "lvshop.lang.name", "const"],
          "loops": 4,
          "rows": 1,
          "cost": 0.00439696,
          "filtered": 100
        }
      }
    ]
  }
}