When it comes to building mobile apps for Android, there are a few languages that are commonly used. As a mobile app development company, you'll want to be familiar with these to create awesome apps for your clients!

1. Java: This is one of the oldest and most widely used languages for Android app development. It's been around for a while, so there's a ton of resources and support available.
2. Kotlin: Kotlin is gaining popularity fast! It's like a modernized version of Java and is officially supported by Google for Android development. Many developers love it for its conciseness and safety features.
3. C++: If you're building performance-critical apps or need to do some heavy lifting with graphics, C++ might be your go-to. It's powerful and fast but can be a bit trickier to work with compared to Java or Kotlin.
4. JavaScript: With frameworks like React Native and Flutter, you can use JavaScript to build cross-platform apps, including Android. It's great for companies looking to save time and resources by building apps that work on multiple platforms.

So, those are the main languages you'll encounter when diving into Android app development. Each has its pros and cons, so it's good to pick the one that fits best with your team's skills and the project's requirements. Happy coding!