Maybe your students have asked you why they should learn a new language. Granted, it takes time and energy. However, there are several positive second language acquisition effects, too.
Students who want to learn a foreign language tend to be more open-minded and extroverted. You as their teacher can use that to wake their interest for other cultures and help them look at the world with different eyes. Here are three easy steps to include foreign cultures into school classes:
Step one: Ask them if they know in which countries the language is spoken. You can use a world map and pin each country or make a list on the chalkboard. Most languages are only spoken in one or maybe two countries but there are some languages (such as English, French, or Spanish) that are spoken in many countries all over the world due to the colonies and migration in former times.
Step two: Let them tell the class what they know about the countries, their inhabitants and culture. Maybe they have special celebrations (like Chinese New Year) or special dishes (like pasta in Italy or paella in Spain). You can collect those pieces of information on the chalkboard. A mind map would be a good means to bring at least some order into the gathered information.
Step three: Collect ideas of topics for future lessons (e. g. bank holidays in Spain, German traditions, Italian food) using the information on the chalkboard. If students choose their own topics, they are likely to pay attention and be motivated. Maybe they can prepare short presentations on various aspects, alone or in groups.