Indeed, there is a subparagraph in the guidance for article 12 that sounds exactly like that. However, it (which can be understood even from the title) only explains the position of the Council of Europe on polygamy: its meaning is that one can get married without being in another marriage.
“Thus, the Court did not find a violation of Article 12 when the State prohibited marriage in its territory between persons, one of whom is in an existing marriage (X v. The United Kingdom, 1970, Commission decision),” reads further in this subparagraph.
The fact that we are talking about a marriage between a man and a woman can be explained very simply: the entire guide to Article 12 is excerpts from the conclusions of the ECHR on previous cases. Two of the cases under review (Johnston and Others v. Ireland and X v. The United Kingdom) involved marriage between different sex partners.
But Zakharova just ignored a separate subparagraph entitled “Sex”, which in the same document follows immediately after “Monogamy” and which refers to the position of the Council of Europe on the issue of same-sex marriage. And it is not surprising, because it says that the Council of Europe can interpret marriage as a union between persons of the same sex.
10. The Court noted that, considered in isolation, the wording of Article 12 could be interpreted so as not to exclude marriage between two persons of the same sex. However, all other substantive Articles of the Convention grant rights and freedoms to “everyone” or state that “no one” can be subjected to certain types of prohibited treatment. Thus, the choice of the wording of article 12 should be considered deliberate. Moreover, the historical context in which the convention was adopted should be taken into account: in the 1950s, marriage was clearly understood in the traditional sense as a union between partners of different sexes (Schalk and Kopf v. Austria, 2010, § 55).
11. The Court examined for the first time whether two persons of the same sex could claim the right to marry in Schalck and Kopf v. Austria and found that Article 12 of the Convention did not impose on respondent States an obligation to grant same-sex couples access to marriage. Although there was no right to same-sex marriage in the Convention, the Court allowed the possibility that, in accordance with the Convention’s nature as a “living instrument”, the right to marry, as enshrined in Article 12, could under no circumstances be limited to marriage between two persons of the opposite sex. … However, at the time, the question of whether to allow same-sex marriage was left to the national law of a Contracting State (Schalk and Kopf v. Austria, 2010, §§ 61-62).
Thus, the Council of Europe ruled that each member state has the right to decide for itself whether to legalize same-sex marriage. However, he decided not to limit the interpretation of Article 12 to marriage between persons of the opposite sex.
We add that the ECHR consistently adhered to this line when considering the case of three same-sex couples against the Russian Federation: it left Russia the right to recognize only a marriage between a man and a woman, but obliged the Russian authorities to develop other forms of partnership that would ensure the rights of same-sex couples. In the notorious business “Schalck and Kopf v. Austria” – the first in the practice of the ECHR, which considered the right of people of the same sex to marry, – the court refused the applicants’ claim precisely because Austria had already passed the Law on Registered Partnership, which gave same-sex couples most marriage rights.