Is it Islamically forbidden for a female teacher to record lessons in her voice with translation and send them to the parents of Muslim and non-Muslim foreign students?

The voice of a woman is not considered 'awrah' (private/concealable) according to the correct scholarly opinion. Therefore, there is no harm in recording lessons and sending them to parents, whether they are Muslims or non-Muslims. However, speech should be limited to what is necessary, and one should avoid softening the voice or anything that could lead to 'fitna' (temptation/strife).