Speaking the local language facilitates understanding of the cultural context. Language can tell you a lot about a community. For example, if it has special pronouns and verbs for people of different genders and ages, one may assume that the understanding of gender and age is probably a pretty complex and nuanced issue in this culture.
One cannot speak all languages though. So, if you lack language competencies, I’d recommend you to develop your ability to observe and build up the experience of observing. Ask questions, pay attention to details, and don't hesitate to ask for feedback. All of that will make your life in the new country more comfortable even if you don’t know the local language.
Pay attention to universal "categories". Regardless of language, people all around the world do things you understand: eating, drinking, sleeping, having fun, working, and interacting with others. There are many categories, you’ll find in any society, including:
- address (formal and informal ways to address people)
- physical contact (How do people say hello, do they keep their distance?)
- gift exchange (Is it customary? What gifs are common? What are the gift-giving traditions?)
- inter-gender and inter-age relations (How do women and men and people of different ages communicate with each other?)
- business communication (Is there a hierarchy and what does it involve?)
- table manners (What’s the proper behavior during mealtime? Are there any traditions or dinner routines?)
The list can go on and on.