SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '4786', '1895', '3096', '3084', '3099', 
    '3103', '3093', '3102', '3101', '3092', 
    '3085', '3090', '3087', '3686', '3089', 
    '3104', '3097', '3094', '3095', '3100', 
    '1870', '1859', 'Y', '1931', '1860', 
    '1881', '1897', '1899', '1898'
  ) 
  AND lang_code = 'en'

Query time 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_feature_variant_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "rows": 29,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variant_descriptions.variant_id in ('4786','1895','3096','3084','3099','3103','3093','3102','3101','3092','3085','3090','3087','3686','3089','3104','3097','3094','3095','3100','1870','1859','Y','1931','1860','1881','1897','1899','1898') and cscart_product_feature_variant_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}