The Hague Convention is not important?

Under Mexico's 1934 nationality and naturalization law, a foreign woman who married a Mexican man was entitled to privileged naturalization, though she could only apply for it after registering her residence in the country.

That Mexican law permitted women to hold dual nationality.

My grandmother married in 1936, while that law was in effect in Mexico. Germany had signed the 1930 Hague Convention on certain questions relating to the conflict of nationality laws. The Hague Convention sought to foster a general understanding regarding national nationality laws, but the country did not ratify it because the Nazi regime came to power shortly thereafter.

By signing the Hague Convention, Germany committed itself not to act in violation of the treaty. However, it appears that pre-1945 laws are not currently regarded as the relevant framework for understanding women's nationality status.