Is my marriage to a French woman, solemnized in a marriage office in Germany with the presence of two witnesses, and then publicly declared in a mosque, considered valid in Islamic law, or must I marry in a mosque with the presence of four witnesses? And is my current marriage considered adultery?

It is permissible to marry a French woman if she is a chaste Muslim, or one of the chaste women from the People of the Book (Jewish or Christian), based on the Almighty's saying: "And chaste women from among the believers and chaste women from among those who were given the Scripture before you." It is a condition to fulfill the requirements of marriage, including the presence of a guardian (wali) and two righteous male Muslim witnesses. If the girl is Muslim, her guardian must be Muslim; otherwise, the ruler or someone delegated by him from among the righteous believers would act as guardian, and a non-Muslim cannot be a guardian. If she is Jewish or Christian, her guardian would be from her own religion. If that is not possible, then the Muslim ruler or the ruler from her own religion would act as guardian, and a Muslim has no guardianship over her unless he is the ruler. Therefore, the marriage contract must be re-contracted if the conditions were not fulfilled.