"xx" meaning in Conventions internationales

{
  "categories": [
    {
      "kind": "other",
      "name": "Nombres en chiffres romains",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Numéraux",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Conventions internationales",
      "orig": "conventions internationales",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_texts": [
    "Composé de la répétition de deux x, chacun voulant dire 10. De même xxx veut dire 30."
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "num",
  "pos_title": "Numéral",
  "senses": [
    {
      "glosses": [
        "20 en chiffres romains minuscules."
      ],
      "id": "fr-xx-conv-num-6Q2C9iev"
    }
  ],
  "word": "xx"
}

{
  "categories": [
    "Nombres en chiffres romains",
    "Numéraux",
    "conventions internationales"
  ],
  "etymology_texts": [
    "Composé de la répétition de deux x, chacun voulant dire 10. De même xxx veut dire 30."
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "num",
  "pos_title": "Numéral",
  "senses": [
    {
      "glosses": [
        "20 en chiffres romains minuscules."
      ]
    }
  ],
  "word": "xx"
}