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 = 'da' 
  AND lang.name IN (
    'text_out_of_stock', 'select_options', 
    'notify_when_back_in_stock', 'enter_email', 
    'enter_email', 'enter_your_price', 
    'contact_us_for_price', 'sign_in_to_view_price', 
    'inc_tax', 'including_tax', 'you_save', 
    'you_save', 'save_discount', 'free_shipping', 
    'save_discount', 'save_discount', 
    'availability', 'items', 'on_backorder', 
    'in_stock', 'availability', 'in_stock', 
    'on_backorder', 'availability', 
    'quantity', 'text_cart_min_qty', 
    'text_edp_product', 'text_out_of_stock', 
    'select_options', 'notify_when_back_in_stock', 
    'enter_email', 'enter_email', 'enter_your_price', 
    'contact_us_for_price', 'sign_in_to_view_price', 
    'inc_tax', 'including_tax', 'you_save', 
    'you_save', 'save_discount', 'free_shipping', 
    'save_discount', 'save_discount', 
    'availability', 'items', 'on_backorder', 
    'in_stock', 'availability', 'in_stock', 
    'on_backorder', 'availability', 
    'quantity', 'text_cart_min_qty', 
    'text_edp_product'
  )

Query time 0.00141

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "45.61"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_ult_language_values",
          "access_type": "system",
          "possible_keys": [
            "PRIMARY"
          ],
          "rows_examined_per_scan": 0,
          "rows_produced_per_join": 1,
          "filtered": "0.00",
          "const_row_not_found": true,
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.20",
            "prefix_cost": "0.00",
            "data_read_per_join": "408"
          },
          "used_columns": [
            "lang_code",
            "name",
            "value",
            "company_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "lang",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "lang_code",
            "name"
          ],
          "key_length": "392",
          "rows_examined_per_scan": 19,
          "rows_produced_per_join": 19,
          "filtered": "100.00",
          "index_condition": "((`eshopuga_upgr_4122`.`lang`.`lang_code` = 'da') and (`eshopuga_upgr_4122`.`lang`.`name` in ('text_out_of_stock','select_options','notify_when_back_in_stock','enter_email','enter_email','enter_your_price','contact_us_for_price','sign_in_to_view_price','inc_tax','including_tax','you_save','you_save','save_discount','free_shipping','save_discount','save_discount','availability','items','on_backorder','in_stock','availability','in_stock','on_backorder','availability','quantity','text_cart_min_qty','text_edp_product','text_out_of_stock','select_options','notify_when_back_in_stock','enter_email','enter_email','enter_your_price','contact_us_for_price','sign_in_to_view_price','inc_tax','including_tax','you_save','you_save','save_discount','free_shipping','save_discount','save_discount','availability','items','on_backorder','in_stock','availability','in_stock','on_backorder','availability','quantity','text_cart_min_qty','text_edp_product')))",
          "cost_info": {
            "read_cost": "41.81",
            "eval_cost": "3.80",
            "prefix_cost": "45.61",
            "data_read_per_join": "7K"
          },
          "used_columns": [
            "lang_code",
            "name",
            "value"
          ]
        }
      }
    ]
  }
}