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

Query time 0.00055

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','3095','3097','3096','3099','3100','3101','3102','3103','3085','3686','3087','3089','3092','3090','3093','3094','3104','3084','1859','1870','Y','1860','1899','1898','1931','1881','1897') and cscart_product_feature_variant_descriptions.lang_code = 'uk'"
        }
      }
    ]
  }
}