Is it permissible to travel to countries where women only cover what is between the navel and the knee for the purpose of da'wah, learning their language, and interacting with them?

It is permissible to travel for the purpose of da‘wah (inviting to Islam), provided that there is segregation between men and women, or that a barrier is present. It is not permissible for a man to directly invite immodestly dressed women; due to the impermissibility of looking at their awrah (private parts). They can be invited through their mahrams (unmarriageable relatives) or through female Muslim callers to Islam.