I'm fairly certain I saw "guys" used to address even women-only groups in American movies and TV.
Conference that wants to be internationally inclusive, which I assume a conference in English held in Germany wants to be, should not ostracize people based on grammar technicalities.
That's just one word, but pronouns in particular differ greatly across languages. Objects can have genders, occupations can have genders, plurals can differ or be the same, etc.. Someone who is not a native speaker can easily make a mistake that is related to gender.
It's always the intent that should be taken into account, not whether someone was offended.
Conference that wants to be internationally inclusive, which I assume a conference in English held in Germany wants to be, should not ostracize people based on grammar technicalities.
That's just one word, but pronouns in particular differ greatly across languages. Objects can have genders, occupations can have genders, plurals can differ or be the same, etc.. Someone who is not a native speaker can easily make a mistake that is related to gender.
It's always the intent that should be taken into account, not whether someone was offended.